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SMITHSONIAN INSTITUTION 
Langley Aeronautical Library 


\ 


\ 












r 


A Practical Aviation 


including 


Construction and Operation 



J. ANDREW WHITE 

U 

Author of “Signal Corps Manual ” 

Director of Vocational Training , Marconi Institute 


A text book for intensive study by men preparing to become skilled 
mechanicians and aviators, containing all the knowledge of fundamentals 
required prior to elementary and advanced flying. 

Each subject is presented by illustration and described completely for 
the reader without turning the page. 

A broad treatment of subjects never before contained in general aeronautic 
text books is included, comprising operation and care of aviation engines, 
reconnaissance, map reading, radio and its uses, machine gunnery and 

bombing from airplanes. 

Designed particularly for individual and class study with an analysis of 
important factors preceding each chapter and a set of review questions 

following every division. 


200 Illustrations 


25 ELM ST. 



NEW YORK 


* 


















TLao 

. IaJ^ 


Copyright 1918 
BY 


WIRELESS PRESS, Inc. 


^c/- 3 dSP' 




Foreword 


It seems to be generally understood that the real value of a textbook’s 
foreword is measured by its helpfulness to the reader in explaining how the 
volume may be studied to best advantage. Almost without exception, what 
is said here in front is supplementary and of a postscript nature, for, para¬ 
doxically, the foreword is written after the manuscript has been completed. 

Seeking to play the game according to the rules, I am forced to two 
conclusions: First, that I have little to say on the grouping of subjects 
and, secondly, that the typographical arrangement requires some explanation 
—perhaps even justification. 

I will dismiss the first by noting merely that the analysis, in skeleton 
form, which precedes each chapter is intended as a guide, aiding dissection 
of the subject into easily remembered parts. These pages are in many ways 
comparable to the instructor’s preliminary talk or a blackboard outline before 
the class takes up co-related subjects in detail. 

To explain, or justify, if you choose, the typographical appearance of 
the pages, necessitates striking the personal note for a minute. The idea 
had its origin in an informal talk with a noncommissioned officer who was 
among the students of an aviation ground school class which I conducted 
at the outbreak of the war. By accident, his notebook came to my hands. 
It was amazingly comprehensive, covering by diagram and data an entire 
series of lectures. When I commended the student for its compilation he 
voiced typically youthful impatience with its limitations. “I try to jot 
down each important thing you say, Sir,’’ he complained, “but I can't seem 
to get them verbatim. The diagrams I copy from the blackboard; that is 
easy. I am never satisfied with my notes, though, because it’s so hard to 
distinguish the vital thing to remember as you go along. Now if I could 
get everything word for word and devise some system of marking so I could 
record the relative emphasis of your voice—well, I’d call that a real notebook.’’ 

That ended the episode. But in it was born the idea which forms the 
basis of this book. By typographical arrangement I have presented military 
aviation as it has been taught in the class room. The diagrams are those 
which have proven most valuable on the blackboard; photographs were 
chosen from among those projected on a screen by balopticon. Supporting 
text explanation of the illustrations has been arranged so the reader is 
never required to turn the page to apply its teachings—each page is a brief 
blackboard talk or illustrated lecture, so to speak. For valuation of the 
importance of statements I have used relative sizes and boldness of type. 

Thus the volume appears as a series of condensed statements, presented 
in a form at variance with usual typographical arrangements, but, I hope, 
an exceedingly useful one. The text is not designed for those merely curious 
about military aviation, nor is it in any sense a treatise on aeronautical engi- 


m 


IV 


Foreword 


neering. The entire book has been written with the idea of possible useful¬ 
ness to student aviators who, rising to a military emergency, have to prepare 
in the shortest possible time. 

It is quite true that flying cannot be learned by reading a book. Tut 
if the “reason why” is made known by the printed word, the process of 
mastering actual airplane manipulation is made shorter and safer for the 
aviation candidate. And in acquiring this understanding of an art which 
is undergoing constant change, best results are attained by concentrating 
on fundamentals. For, once a sound knowledge of aerodynamic principles 
and elements of design is acquired, the constant technical changes in aircraft 
and their employment—even those advances which at first glance appear 
revolutionary—may be easily understood. 

That is why, in the pages following, no particular type of airplane con¬ 
struction has been emphasized, no special motor featured. Where a method 
of control or use of an airplane has been explained, the endeavor has been 
to select the practice which presents the basic principle upon which 
modifications rest. 

A Review Quiz follows each chapter. The questions are purposely not 
exhaustive. Each one is designed, however, to start a train of thought in 
the mind of the reader which will encourage him to turn back and dig into 
parts of the text which he may have skipped over too lightly. 

It may also be noted that the decorative style of writing has been 
diligently repressed. More than once in preparing the manuscript the 
temptation arose to illustrate a point by a humorous or dramatic anecdote; 
but in all instances it was regretfully set aside. The method of presentation 
demanded concise statement, else the reading matter essential to under¬ 
standing of the illustrations would have carried over the page. 

Widely varied aspects of flying are treated in the fifteen chapters; in 
many of these the consensus of best obtainable opinion has ruled in the , 
absence of finally established practice. In fact, all through the text the 
opinion of General Sir David Henderson has been borne in mind, that: 
“There are no experts in military aeronautics. There are experts in the 
various branches: in flying, in scientific research, in the design and con¬ 
struction of airplanes and engines, in military organization and tactics.” 
In consequence of which many practical men have been consulted in the 
endeavor to place into this volume the best thought of specialists in each 
subject. Since aviation still remains in a transitory stage from an art to a 
science, further comment from readers will be cordially welcomed and care¬ 
fully weighed with a view to improving future editions. 

In conclusion, I should like to acknowledge the assistance of Mr. William 
J. Hernan and Lieut. Marius Mignot in supplying for the terms defined in 
the nomenclature French equivalents and their phonetic pronunciation. With 
generous thanks also to the many others who criticized the book in manu¬ 
script form, I send the volume on its journey to make its bid for approval on 
the sincerity with which it was written—solely, simply and finally for 
military aviators, to whom it is dedicated with the hope that it will be useful 
in their preliminary and supplemental study to the ultimate end of 
becoming qualified airmen. 


J. ANDREW WHITE. 




Contents 


CHAPTER I 

Theory and Principles of Flight. 1 

Types of Airplanes—Helicopter and Ornithopter—Pusher and Tractor— 
Monoplane, Biplane and Triplane—Axes of Rotation—Principle of Flight— 

Lift by Air Pressure and Suction—Lift and Drift—Lift-Drift Ratio—Angle 
of Incidence—Camber—Aspect Ratio—Stagger. 

CHAPTER II 


Elements of Airplane Design. 13 

Factors of Superiority in Design—Climbing Rate—Greatest Speed—Hori¬ 
zontal Equivalent—Design for Maximum Climb—Design for Maximum 
Velocity—Angles of Incidence in Flight—Minimum—Optimum—Best 
Climb—Maximum. 


CHAPTER III 


Flight Stability and Control. 21 

Airplane Equilibrium—Stability—Longitudinal Stability—Lateral Stabil¬ 
ity—Directional Stability—Center of Gravity—Washout and Washin—Aile¬ 
rons—Banking—Controls—Wheel and Column—Joystick. 

CHAPTER IV 

Materials, Stresses and Strains. 33 

Action on Materials—Stress—Strain—Factor of Safety—Stress and Strain 
Forces—Strength of Wood Under Stress—Wood for Airplanes—Wing 
Covering—Fabric—Dope—Metal Fittings and Wire. 

CHAPTER V 


Rigging the Airplane. 41 

Erection and Assembly—Landing Gear—Horizontal Stabilizer—Vertical 
Stabilizer—Rudder—Elevators—Assembly of Lifting Surfaces—Alignment— 
Over-all Adjustments—Control Cables and Wires—Effect of Alignment Er¬ 
rors—Flight Defects. 


CHAPTER VI 

Fundamentals of Motive Power. 51 

The Propeller—Balance—Care—The Gasoline Engine Cylinder—Combus¬ 
tion Chamber—Piston—Connecting Rod—Crank Shaft—Revolution—The 
Four-Cycle Principle—Multiple Cylinder Engines—4-Cylinder Operation— 
6-Cylinder Operation. 


CHAPTER VII 

Pistons, Valves and Carburetors. 63 

The Piston 1 —Crank Shaft—Crank Case—Valves and Valve Mechanism— 
Camshaft—Cams—Valve Operating Mechanism—Valve Clearance—Car- 
buretion—Principle of the Carburetor—Construction. 

CHAPTER VIII 


Ignition, Cooling and Lubrication of Engines. 73 

Ignition—Magneto—Distributor—Condenser—Circuit Breaker—Spark Plug 
—Cooling—Water Cooling—Air Cooling—Lubrication — Splash — Force 
Feed. 


V 










CHAPTER IX 


Types of Motors, Operation and Care of Engines. 79 

Bore and Stroke Ratio—V-Type Motors—8-Cylinder—12-Cylinder—The 
Liberty Motor—Rotary Engines—The Gnome Engine—Starting the Engine 
—Fuel Conservation in Flight—Care of Engines—General Rules—The 
Trouble Chart. 

CHAPTER X 

Instruments and Equipment for Flight. 95 

Aviator’s Equipment—Clothing—Safety Belt—Airplane Instruments—Scope 
and Usefulness—Cockpit Arrangement—Gauges—Compass—Barometer or 
Altimeter—Tachometer—Angle of Incidence Indicator—Inclinometer— 

Drift Meter—Air Speed Meter—Banking Indicator. 

CHAPTER XI 

First Flights and Cross-Country Flights. 103 

Instruction in Flying—First Flights—Right of Way—Landing—Use of the 
Compass—Compass Error—Adjusting the Compass—Laying Off a Course— 

Data Required—Radius of Action—Some Flight Considerations—Lost 
Bearings—Landmarks—Time Checking—Forced Landings—Re-Starting— 

Map Reading—The Flying Crew—The Repair Crew. 

CHAPTER XII 


Aerobatics and Night Flights. 127 

Advanced Flying—Spiral—Nose Dive—Spinning Nose Dive—Aerobatics— 

Loop the Loop—Vertical Bank—Zooming—Roll Over—Spiral Loop—Im- 
melman Turn—Night Flying—Preliminary Instruction—Landing at Night. 

CHAPTER XIII 


Meteorology for the Airman. 137 

Characteristics of the Air—Atmospheric Pressure—Pressure Areas—Cy¬ 
clone Area—Anti-cyclone Area—Line Squalls—Beaufort Scale—Wind Con¬ 
ditions Which Affect Aviation—Aerial Fountain—Aerial Cataract—Wind 
Layers—Wind Gusts and Eddies—Clouds and Their Significance. 

CHAPTER XIV 

Aerial Gunnery and Combat—Bombs and Bombing. 147 

Combat Airplanes—Factors of Success in Air Combat—The Lewis Machine 
Gun—Accuracy and Volume of Fire—Ammunition and Fire Correction— 

Gun Mountings and Fire Radius—Fighting in the Air—Aerial Tactics— 
Contact Patrol—Anti-Aircraft Fire—Bombing Air Raids—Types of Bombs 
—Bomb Dropping—Use of the Range Finder. 

CHAPTER XV 

Reconnaissance and Fire Spotting. 171 

Reconnaissance by Airplane—Orders for Reconnaissance Flights—Tactical 
Reconnaissance—Estimates of Enemy Strength—Strategical Reconnais¬ 
sance—Reports of Flights—Instruction in Code Telegraphing—Proper Grip 
on the Key—Sending—Receiving—Directing Artillery Fire—Types of 
Shells—Ranging—Observer’s Map and Code Signals—Signals from the 
Ground—Radio (Wireless) Telegraphy—Airplane Radio Apparatus—Aerial 
Photography. 


APPENDIX 

Nomenclature of Aeronautical Terms—French Equivalents—Phonetic Pro¬ 
nunciation—Metric Conversion Tables—Rules for Mensuration. 


Vl 















Vlll 


Practical Aviation 


CHAPTER ANALYSIS 

The Theory and Principles of Flight 

TYPES OF AIRPLANES: 

(a) Helicopter. 

(b) Ornithopter. 

(c) Tractor. 

(d) Pusher. 

(e) Monoplane. 

(f) - Biplane. 

(g) Triplane. 

AXES OF ROTATION: 

(a) Pitching. 

(b) Yawing. 

(c) Banking. 

THE PRINCIPLE OF FLIGHT: 

(a) Air Pressure. 

(b) The Aerofoil. 

(c) Camber. 

(d) Chord and Span. 

(e) Angle of Incidence. 

LIFT BY AIR PRESSURE AND SUCTION: 

(a) Lift. 

(b) Drift. 

(c) Lift-Drift Ratio. 

(d) Velocity. 

(e) Flow of Air. 

(f) Aspect Ratio. 

(g) Stagger. 



CHAPTER I 


The Theory and Principles of Flight 


It is natural for the student aviator to be more or less impatient with 
the technical side of aviation. He is anxious to fly immediately, and rather 
disposed toward acquiring - his knowledge of fundamentals at some later date. 
This mental attitude must be overcome; many tragic occurrences have had 
their origin in impatience. 

The military aviator’s success largely depends upon his acquaintance 
with the essential features of airplane design—why the machine flies and 
what makes it stable. Safety in maneuvering in air battles and flying effi¬ 
ciency is based on knowledge of the theory of dynamic flight and the limita¬ 
tions of his machine. The noticeably exaggerated movements of controls by 
students in first flights, too, are due not alone to nervousness, but to igno¬ 
rance of the sensitiveness of the control surfaces, all of which function in 
accordance with flight laws. 

Theoretical knowledge is necessary. That it can be satisfactorily ac¬ 
quired by textbook study has been demonstrated and it is expected that the 
reader will begin the study of these pages with a firm conviction that the 
prospective aviator must be thoroughly grounded in fundamentals. 

Military airplanes will of course be given first consideration. Some 
aeronautical generalities are necessary, however, in dealing with design and 
construction, but these will be treated briefly. 

The airplane is but one form of flying machine. Leaving balloons of 
various types entirely outside the question, there still remain three types of 
heavier-than-air machines. While study will be concentrated on the airplane, 
passing reference should be made to the other two types before proceeding. 
These are: 

The Helicopter —a machine which employs the principle of direct lift by 
means of an air screw propeller operating on a vertical axis. This is not a 
practical type of flying machine and little has been done with it. 

The Ornithopter —a machine which derives its name from the bird, its 
principle being the creation of flapping wings given a reciprocal motion 
somewhat similar to rowing, the forward push intended to exactly counter¬ 
feit that of the bird’s wings. These machines are not yet successful. 

The reader may be fascinated by the possibilities of research into the 
field represented by this latter type, but considering the present efficiency of 
the airplane, it is safe to assume that time will be better spent in utilizing its 
man-discovered principles of flight, rather than in following a new line of 
thought on the assumption that Nature never makes a mistake and the bird 
is therefore the best model. 

It must be remembered that flying is but an incident in the life of a bird, 
just as walking is to a man. The famous aviator Santos-Dumont drew a 

1 


2 


Practical Aviation 


r 

| * 

I 





An airplane of the “tractor” type, so called because the propeller is attached to the front, 

pulling the machine through the air 


parallel which disclosed the folly of blindly following Nature, when he 
pointed out that such a procedure would have resulted in locomotives being 
built with huge iron legs and steamships with the flapping fins and lashing 
tail of the whale. Sir Hiram Maxim further blasted the bird-flight theory 
by noting that “in order to build a flying machine with flapping wings, to 
exactly imitate birds, a very complicated system of levers, cams, cranks, etc., 
would have to be employed, and these of themselves would weigh more than 
the wings would lift.” 

Without further comment, therefore, the study will be confined to the 
airplane, the most successful type of aircraft and the best developed means of 
navigating the air. 

The airplane is sustained by the upward push of the air flowing past it; 
it therefore is composed of (a) lifting surfaces, (b) power for propulsion. 

Propulsion through the air is effected by a propeller, identical in prin¬ 
ciple though not in appearance, to the screw on a boat. An engine drives 
this propeller at the required velocity. The propulsion produced by the pro¬ 
peller is called the thrust. 

When the propeller is attached to the front, pulling the machine through 
the air, the airplane is called a tractor. 

If the propeller is back of the wings, or main lifting surfaces, the airplane 
is called a pusher. 

The tractor type, with a single propeller, is generally acknowledged 
the most efficient all-round machine, although pushers with two air screws 
have distinct values in gun-carrying machines. 

An airplane with two wings, one above the other, is known as a biplane. 

One with three wings is called a triplane. 










Types of Airplanes 


3 



A “pusher’ biplane until the propeller back of the wings or main lifting surfaces and the 

pilot’s seal directly in front 


The single wing type, with one lifting surface, is called a monoplane. 

The tractor biplane is the type which is more nearly standardized and will 
be principally considered here. 

The main lifting surfaces are planes, or “wings,” which present their 
widest dimension across the line of flight and create the air compression on 
their surfaces which produces flight. 

The body to which these planes are attached is known as the fuselage, 
the engine and seats mounted in it being enclosed to lessen the resistance of 
the wind. 

In pusher types the body is called the nacelle. 

Since the airplane “sails” through the free air, it has three axes of rota¬ 
tion. 

(1) It may ascend or descend. This is known as pitching, and is con¬ 
trolled by depressing or elevating an elevator by means of suitable controls. 

(2) It may change its direction of travel, or steer to right and left. 
This is called yawing, and is made possible by the operation of the rudder. 

(3) It may tip over to either side, a movement termed banking or roll¬ 
ing. This lateral motion is offset by three means of control which give a dif¬ 
ference in angle to the two sides of the wing surface, causing one side to lift 

more than the other. The controls are: (a) ailerons, small planes set at 
each side, between and independent of the main lifting surfaces; (b) wing 

flaps, also called ailerons, which are hinged portions of the main planes; (c) 

zuarping, or twisting the main lifting surfaces to simultaneously lessen and in¬ 
crease the angle of inclination to the wind as required on both sides. 


























4 


Practical Aviation 



THE PRINCIPLE OF FLIGHT 

The upward air pressure against its main wing surfaces enables the 
airplane to fly, when these wing surfaces, or planes, are set at an angle 
inclined from the direction of motion, the pressure being supplied by the 
speed at which the planes are driven by the propeller. 

AIR—Air is attracted by the mass of earth, or the gravity force, and therefore 
has weight. A cubic foot of dry air, at sea level and 32 degrees Fahrenheit tempera¬ 
ture, weighs 0.0807 lb. Its density decreases with altitude, until at a mile above sea 
level it weighs 0.0619 lb., and at five miles, 0.0309 lb. per cubic foot. 

Air also has motion, which must be taken into consideration by the aviator, and 
resistance, due to density and intensity of motion, or wind. Air resistance comprises: 

Inertia —Its tendency to remain at rest, if still; in motion, if moving. 

Elasticity —Its tendency to reoccupy its normal amount of space after being dis¬ 
turbed. 

Viscosity —The tendency of particles of air to resist separation. 

Inertia gives the propeller its “hold” in the air; elasticity, when air is compressed 
under the surface of the plane, aids the lift; viscosity creates friction, which is min¬ 
imized by using polished surfaces and stream-lining airplane parts. 

THE SURFACE 

A wing surface is meant by this expression (see Figure 1). It has a 
strictly aeronautical designation, viz.: 

THE AEROFOIL 

This term is seldom used by aviators, but is commonly employed by 
aeronautical engineers to differentiate between an ordinary surface and one 
inclined at an angle to the direction of motion, having thickness, and curved 
to secure a reaction from the air for lifting. 

CAMBER 

This is the term which designates the curvature of the surface, or 
aerofoil. 















Definitions of Wing Terms 


5 



THE CHORD 

This is the dimension of an imaginary straight line from the front edge 
of the aerofoil, or surface, to the rear edge, as shown by A — B, in Figure 2. 

The front edge of the wing is known as the leading edge, and the rear 

as the trailing edge. 

SPAN 

This is the dimension of the surface across the direction of motion, indi¬ 
cated by A —C, in Figure 2. 

THE ANGLE OF INCIDENCE 

This is the angle of inclination of the chord to the air stream. 

In practice this is the angle of inclination of the chord to the line of the 
propeller thrust. If the leading edge of a surface is above the trailing edge 
when driven through the air, the angle of incidence is positive. A surface 
with the trailing edge presented above the leading edge, or negatively to 
the air flow, would bring the air pressure to the top of the surface and con¬ 
stitute a negative angle. 

LIFT BY AIR PRESSURE AND SUCTION 

"File airplane wing having been considered as a surface, its action upon 
the air may be described. 

Air, or the atmosphere, has characteristics similar to water, the atmos¬ 
phere being an ocean of definite extent and pressure at different altitudes, 
and flowing past an object either in stream lines, or in broken up eddies due 
to disturbances in its flow. 



























6 


Practical Aviation 



Figure 3 —Action of air on the aerofoil 


The nature of the air pressure when encountering the aerofoil is shown 
in the drawing, Figure 3. 

The under face of the airplane wing compresses the air, resulting in a 
positive force. 

At the same time a suction is caused by the air flowing past the upper 
face, causing a partial vacuum, tending to draw the surface upward. 

The value of this suction is about three-fifths of the total pounds force 
of the air’s action on the aerofoil. The factors of this air reaction are: 

(a) The mass cf the air. 

(b) The velocity of the aerofoil. 

The reaction increase is as the square of the velocity. 

The air reaction has two values: 

LIFT—opposed to gravity, or the airplane’s weight. 

DRIFT—opposed to the thrust of the propeller. 

The lift is opposed by the drift, which must be overcome by the thrust 
supplying velocity great enough to produce an air reaction sufficient to pro¬ 
duce flight. 

Drift is of three kinds: (a) active drift, produced by the velocity of the lifting 
surfaces; (b) passive drift, the resistance of other parts of the airplane, such as struts, 
wires, tank, fuselage, hood, etc.; (c) skin friction, or the air resistance on roughness 
of surface. 

LIFT AND DRIFT 

It has been shown how the air pressure is created on a surface inclined 
at a positive angle to the direction of motion, and that this pressure exerts 
a lifting force. 

The air pressure is inclined upward and to the rear of the direction of 
motion in a ratio equal to the variance of the angle of incidence of the wing 
plane. 

The vertical action of the air pressure is a force capable of lifting weight 
but its horizontal component of air pressure represents resistance to motion. 

Thus, while 

LIFT is a vertical air pressure. 

DRIFT, its horizontal component, is resistance. 













Lift-Drift Ratio 


7 





Figure 4 



- Direction of - 

motion 

Figure 5 

LIFT-DRIFT RATIO 



Figure 6 


Flight is maintained by the proportion of lift to drift being sufficiently 
great to overcome the force of drift. The characteristics of the wing surface 
are designed for the greatest lift with the smallest consequent drift, so that 
minimum power supplies maximum capacity for load carrying. 

The factors to be considered in determining lift-drift ratio are velocity, 
angle of incidence, camber and aspect ratio. 

VELOCITY 

Drift increases to lift proportionately with increase of velocity. 

Active drift, formed by the wing surfaces, is a component part of the 
air reaction which creates the lift, and therefore increases as the square of 
the velocity. At all speeds the efficiency of the airplane would remain the 
same, but for the 

Passive drift, or the resistance of the airplane parts other than the lifting 
surfaces, which also increases as the square of the velocity, yet adds nothing 
to the lift. Thus by adding its resistance to the active lift, it prevents the 
airplane’s ratio of lift to drift from increasing proportionately with the in¬ 
crease of the thrust. In other words, the efficiency of the airplane would not 
decrease with added velocity, if it were not for the passive drift. This 
factor prevents, so to speak, doubling the speed or lift by doubling the thrust. 

To diminish the passive drift all parts of the airplane are given stream 
lines, or a form offering least resistance as they pass through the air. 

Head resistance is a term formerly employed to described passive drift. It has 
been largely discarded, however, for its inaccuracy of description of the effect of the 
action of parts in air reaction. Passive drift is due more to the action on the rarefied 
area behind the object than to the head or forward part of hood, struts, wires, etc. 

FLOW OF AIR 

Figures 4, 5, 6 illustrate the flow of air around three objects of varying 
form. 

In Figure 4 the rarefied area, or drift, is represented by D — D, and is of 
marked extent. 

In Figue 5, this area, indicated by the same symbol, has decreased, the 
air flowing closer to the spherical body. 

Figure 6 shows the rarefied area still further diminished, the shape of the 
body being conducive to closer air flow. 

These three figures illustrate the importance of stream-lining parts on 
the line of flight. 

As the head resistance is increased by the rarefied area in the rear of 

the object, the thrust required increases proportionately. 

The action of air on objects of different shapes and propelled at varying veloc¬ 
ities is determined by visualizing the air in laboratory research with wind tunnels. 


















8 


Practical Aviation 


ANGLE OF INCIDENCE 

This is the angle of inclination of the chord to the air stream. Its effi¬ 
ciency varies and is determined by what is desired in thrust, weight-carrying 
capacity, and ratio of climb to velocity. 

It may be accepted as a general premise that the greater the velocity 
the smaller should be the angle of incidence, so that the rarefied area may 
be kept to stream-lines and the eddies of air reduced to a minimum. These 
eddies represent drift, since they have no lift, and when produced by too 
great an angle of incidence, the power required to produce them is wasted, 
with consequent loss in efficiency of the airplane. 

Wind tunnel research largely determines the best angles of incidence. 


CAMBER 

The purpose of the camber, or curve, in a lifting surface is to decrease 
the active drift, horizontal component of the lift. 


Camber of lower face —The horizontal air reaction from a flat surface 
would be considerable and increase the drift. Curving the wing surface 
compresses and accelerates the air from the leading edge to the trailing 
edge. If this air action is not uniform the drift will be increased. 


With a fixed upper face, an increase in the camber of the lower face does not 
greatly vary the relation of lift to drift, but lift increases with camber increase. Most 
of the lift is furnished by the upper face, however, and the camber increase of the 
lower does not produce sufficient effect on the upper to compensate for the lessened 
depth of spar allowed when a rather flat surface is used. Decreased depth of spar per¬ 
mits a weight reduction in the framework of the wing without sacrifice of strength. 
It is for this reason that lessened camber for the under side is allowed. 


Camber of upper face —The top surface is curved to produce the least 
possible eddies of air resistance behind the trailing edges, the rarefied area 
produced being given the best obtainable stream line to lessen the drift in 
the lift-drift ratio. 


Velocity, angle of incidence and thickness of aerofoil, or surface, deter¬ 
mines the camber of the upper face. In general, the camber and angle of 
incidence should decrease proportionately with velocity increase. 


On an aerofoil with a flat under face the maximum lift increases with the upper 
face cambered up to 1/15, beyond which it decreases. Improvement of the lift-drift 
ratio is steady up to 1/20 camber, thereafter showing decrease in value with deeper 
cambers. 


With the under face cambered the increase of upper face camber above 1/15 shows 
little variation in lift, but steady increase of drift. 






Aspect Ratio 


9 



ASPECT RATIO 


The proportion of span to chord is the aspect ratio. The total span 
divided by the chord of the wings is the “aspect” of an airplane. 


In Figure 7 the span is 36 feet, the chord is 6 feet, the aspect ratio is 
therefore 6 to 1. 

Figure 8 shows a span of 30 feet and a chord of 10 feet, an aspect of 3. 

At a given velocity and given wing area, the reaction increases with 
increase in aspect ratio. The reason for this is that a greater mass of air is 
engaged with a wider span, the reaction of air being partly the result of the 
mass of air engaged. 

An average aspect for an airplane is 6, but in deep cambered planes an aspect of 
9 is considered practicable by designers. 

The usual limits are 2 to 8. High speed airplanes of the pursuit type seldom ex¬ 
ceed an aspect ratio of 5. 


In a general way it may be said that the higher the aspect ratio, the 
better is the lift-drift ratio. But with decrease of chord the deepening of the 
camber requires added thickness of aerofoil, or surface, and in practice the 
reduction of chord required for an extremely high aspect ratio makes pro¬ 
hibitive the use of the thickness of surface which would give the best camber. 


The “spill” of the air from under the tips of the wings also has some 
bearing on aspect ratio, since with wings of small span this loss in lift is 
material, whereas in wings of wide span the percentage is small and the 
loss inconsequent. It is because of the slight lift gained in proportion to 
the air disturbance that wing tips are rounded off in many airplanes. 



































10 


Practical Aviation 






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Figure 9 —The upper plane placed in advance of the lower, or staggered 


STAGGER 


When the top surface of a biplane is placed in advance of the vertical 
with relation to the lower wing surface, the term stagger is used. 


See Figure 9. 


By staggering the upper plane ahead of the lower plane it is removed 
from the area of action of the lower aerofoil and engages undisturbed air. 

. 4 

Without stagger, the confusion of air reaction could be obviated by 

increasing the gap between upper and lower planes a dimension equal to \ l / 2 
times the chord. But the length of struts and wires required for this open¬ 
ing increases the drift, making it impracticable to have a gap much greater 
than the chord. 

* 

• 

Minor considerations of construction and balance, and visibility for pilot 
and observer, govern the proportion of stagger, although, theoretically, the 
upper plane should be advanced a distance about equal to 30 per cent, of the 
chord, small ■ variations being further governed by velocity and angle of 
incidence. 











Practical • Aviation 


11 




REVIEW QUIZ 


Theory and Principles of Flight 

1. Describe three types of heavier-than-air machines and state their 

practicability. 

2. Define three main divisions in the uses of military airplanes which 

govern types. 

* 

3. State the fundamental principle which makes flight possible. 

4. What is meant by the inertia of air? 

5. What is the aeronautical term for a wing surface, and how does it 

differ from an ordinary surface? 

t * 

6. Define camber. 

^ ' 

7. How is the dimension of the chord of an airplane taken? The span? 

8. Give a full definition of the angle of incidence. 

9. In what way does atmosphere resemble water? 

10. What is the action on air when it encounters the under face of the 

aerofoil? 

11. State what proportion of lift is represented in the partial vacuum 

above the upper face. 

12. What are the two values of air reaction? 

13. Define three kinds of drift. 

14. What is lift-drift ratio and how a~e the characteristics of the wing 

surface governed by it? 

15. State the four factors to be considered in determining lift-drift ratio. 

16. Define two kinds of drift created by velocity and state how these 

affect flight efficiency. ** ^ 

17. Show by a simple diagram why head resistance requires proportion¬ 

ate thrust increase. 

18. In what way does increased velocity affect the angle of incidence? 

19. What is the purpose of the camber and why should upper and lower 

faces differ? 

20. What is meant by an airplane’s aspect ratio? 








12 


Practical Aviation 


CHAPTER ANALYSIS 

Elements of Airplane Design 

FACTORS OF SUPERIORITY IN DESIGN: 

(a) Climbing Rate. 

(b) Greatest Speed. 

(c) Horizontal Equivalent. 

(d) Design for Maximum Climb. 

(e) Design for Maximum Velocity. 

ANGLES OF INCIDENCE IN FLIGHT: 

(a) Minimum. 

(b) Optimum. 

(c) Best Climb. 

(df Maximum. 




CHAPTER II 



Elements of Airplane Design 

% 

The military aviator can insure proficiency only through acquisition of 
a sound knowledge of the characteristics of design which govern the con¬ 
struction of an airplane. Air tactics in warfare, while a subject for military 
experts, are insolubly a part of the mechanics of aeronautics. While the 
manner of conducting air battles is subject to daily changes, it must be re¬ 
membered that the effective observer or air fighter who creates new evolu¬ 
tions is logically one whose knowledge of engineering features of design is 
sound. Skill in manipulation of controls is essential of course, but it can 
readily be recognized that attempted creation of new tactics might well be 
fatal unless an aviator has an intelligent understanding of the limitations of 
his machine and what it can accomplish within the safety factor. 

In this chapter some consideration will be given to the factors upon 
which a military airplane must base its superiority. 

In the preceding chapter fundamental principles of flight have been 
given; it now devolves upon the student to recognize that in military use of 
flying machines two important features are encountered: 

(a) Superiority in climbing rate. 

(b) Greatest speed. 

It is obvious that the machine which excels in speed and ability for fast 
climb will be most effective against the enemy. An airplane which attains 
speed at the sacrifice of climbing ability can be out-maneuvered by fast¬ 
climbing enemy aircraft in air battles, and the same is true of reverse quali¬ 
ties of climb versus speed. The combination of great speed with maximum 
climb is the ideal striven for in military airplane design. 

As in all mechanical devices, however, the ideau’must be subjected to 
compromise, and it is now purposed to apply the knowledge of fundamentals 
previously gained to consideration of the engineering factors which govern 
the design of machines for maximum climb and greatest velocity. 

Thus far the reader should bear in mind that the airplane is being studied 
in two distinct divisions; viz., the lifting surfaces and the propelling mech¬ 
anism, or (a) the airplane structure, (b) engine and propeller. 

In the preceding chapter the factors of lift-drift ratio were outlined and 
commented upon. As a thorough knowledge of the proportion of lift to drift 
is essential to an aviator, further considerations of design will be mentioned. 


13 


14 


Practical Aviation 



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Horizontal Equivalent 


15 



Figure 10 —Lifting surfaces of same area but different horizontal equivalent 


The efficiency of the airplane structure is determined by the lift-drift 
ratio, and an additional item in relation to lifting surfaces which must be 
considered is: 

HORIZONTAL EQUIVALENT 

This is determined by the arrangement of lifting surfaces and is im¬ 
portant because lift (vertical component of the reaction) varies as the hori¬ 
zontal equivalent of the surface, but drift remains the same. That is, with 
reduction in horizontal equivalent (H. E.) of aerofoil the ratio of lift to drift 
is lessened. 

Figure 10 gives front views of two lifting surfaces. 

Both have the same surface area, but the upper, having its full horizontal 
equivalent, has the best lift-drift ratio. 

The lower surface, being inclined from its center, has lessened IT E. 
and in consequence less lift. 

Therefore, as the lower surface containing the same area as the upper 
surface, produces the same amount of drift, but less vertical lift, its lift-drift 
ratio is less than the upper’s. 

Sacrifice of efficiency in lift-drift ratio is often made to gain lateral stability; such 
employment of surfaces tilted from the center will be considered later. 












16 


Practical Aviation 



Airplane design is restricted by opposing essentials which require the 
aerofoil (lifting surface) characteristics and velocity to produce either Maxi¬ 
mum Climb or Maximum Velocity. A compromise between the two is rep¬ 
resented in all airplanes. 

DESIGN FOR MAXIMUM CLIMB 

The factors in an airplane designed for maximum climb are: 

(a) Large aerofoil. 

(b) Low velocity. 

(c) Large angle of incidence to propeller thrust. 

(d) Large angle relative to direction of motion. 

(e) Large camber. 

(a) LARGE AEROFOIL—A large area of lifting surface is required to 
engage the mass of air necessary for flight with a lozv velocity. 

(b) LOW VELOCITY—Speed must be sacrificed to secure the best lift- 
drift ratio. 

(c) LARGE ANGLE OF INCIDENCE TO PROPELLER THRUST— 
The most efficient airplane is one with inclined lifting surfaces propelled by hori¬ 
zontal thrust, therefore a flying machine for maximum climb to be driven along 
an upward sloping path with propeller thrust horizontal has its aerofoil at a large 
angle to the direction of the thrust. 

See A — A 1 Figure 11. 

In the preceding chapter it was shown that the lift-drift ratio falls with increased 
velocity where the angle of incidence is great, because with a large-angled aerofoil 
increased speed creates more eddies in the air reaction. These air reactions require 
power to produce them, yet they have no lift value; they therefore represent drift and 
lower the lift-drift ratio. 

(d) LARGE ANGLE OF INCIDENCE TO DIRECTION OF MOTION 
—With lozv velocity the angle’s relation to the direction of motion should be large. 

See A — B, Figure 11. 

(e) LARGE CAMBER—With low velocity and large angle cf incidence 
the camber of the aerofoil should be large. 



























17 


Design for Maximum Velocity 



The airplane designed mainly for speed has a small margin of lift at 
low altitudes when its propeller thrust is horizontal. In the rarefied atmos¬ 
phere of higher altitudes engine efficiency is lowered and the margin of 
lift disappears. Then only horizontal flight is possible. Flying thus with 
its thrust horizontal it is at maximum efficiency, if loss of engine and pro¬ 
peller efficiency is not considered. 

DESIGN FOR MAXIMUM VELOCITY 

The factors in an airplane designed for maximum speed with given 
surface and power are exactly opposite the requirements for maximum 
climb. Thus: 

(a) Small aerofoil. 

(b) High velocity. 

(c) Small angle of incidence to propeller thrust. 

(d) Small angle relative to direction of motion. 

(e) Small camber. 

(a) SMALL AEROFOIL—By its increased velocity the speedier propelled 
surface engages a greater mass of air in a given time and the required lift is 
secured with smaller surface. 

(b) HIGH VELOCITY—Lessened aerofoil angle produces less drift, and 
velocity may be increased without loss in lift-drift ratio. 

(c) SMALL ANGLE OF INCIDENCE TO PROPELLER THRUST— 
As both propeller thrust and direction of motion are horizontal, a small angle of 
incidence is most efficient for speed. 

(d) SMALL ANGLE OF INCIDENCE TO DIRECTION OF MOTION 
—Where velocity is a consideration paramount to lift, a small angle of incidence 
is most efficient. 

(e) SMALL CAMBER—Lessened camber at high velocity produces the 
best lift-drift ratio. 

The airplane built in accordance with the above is intended to possess only suf¬ 
ficient lift to get off the ground. The types illustrated on this and the preceding page 
are extremes, but the compromise, an airplane with climb and velocity made equal con¬ 
siderations, i.e., a practical all-around type, is designed by consideration of the factors 
disclosed in these examples. 






























18 


Practical Aviation 



Figure 13a —Minimum angle 


Figure 1 3b—Optimum angle 


In the illustrations on this page an airplane of practical utility is shown 
at varying angles of incidence while in flight. 

At low altitudes the aircraft shown has slight margin of lift when the 
thrust is horizontal. 

The fighting machine usually flies at an altitude where maximum velocity 
is gained at sacrifice of maximum lift. It is obvious that with slight margin 
of lift at low altitudes, the margin of lift disappears with the rise of the 
airplane, because of loss of engine power in the rarefied air. But when the 
machine arrives at the altitude where horizontal flight is just possible, it is 
given its maximum velocity because, even though engine and propeller 
efficiency is lowered, the margin of lift has disappeared and the surfaces are 
at their best flying efficiency for horizontal flight. 

ANGLES OF INCIDENCE IN FLIGHT 

Minimum—(See Figure 13a). The angle of the aerofoil is the smallest 
at which, with amount of power and area of surface fixed, the machine can 
maintain greatest velocity in horizontal flight at low altitudes. 

An airplane having less camber and smaller angle of incidence, i.e., so designed 
that the margin of lift is negligible, or just sufficient to maintain horizontal flight, would 
attain greater velocity with the same surface area and power. 

Optimum—(See Figure 13b). Here the axis of the propeller is hori¬ 
zontal and the angle of incidence that which is required for best lift-drift 
ratio. Velocity is lessened at this angle, at which slight climb is developed 
at low altitudes. 

Best Climb—(See Figure 13c). This angle is about midway between 
maximum and optimum angles of incidence. Here the increased angle has 
added to the drift and thereby decreased the velocity. 

With the angle fixed, a decrease in velocity lessens the drift, but where the angle 
has been increased the lift thereby gained in a measure offsets the loss in lift through 
lessened velocity. 

Beginners should never exceed the angle of best climb. 

Maximum—(See Figure 13d). Horizontal flight is just possible at this 
angle, because drift has been greatly increased and velocity materially les¬ 
sened in consequence. 

If the angle were further increased the lift-drift ratio would be so lozuered 
that the lift would be less than the weight and the airplane would fall. This 
fall is known as the “pancake 
































Practical Aviation 


19 


REVIEW QUIZ 

Elements of Airplane Design 

1. Why is a knowledge of design valuable to the military aviator? 

2. State the combination of qualities which represents the ideal in mili¬ 

tary airplanes. 

i 

3. Define horizontal equivalent. 

4. What change is effected in the lift-drift ratio when horizontal 

equivalent is reduced? 

5. For what reason is a sacrifice of efficiency in lift-drift ratio often 

made? 

6. Name the factors of design which produce an airplane for maximum 

climb. 

7. Why is a large aerofoil required with low velocity? 

8. Should the aerofoil’s angle of incidence be great or small for climb¬ 

ing? / 

9. What should be its relation to the direction of motion when climb¬ 

ing? 

10. State when an airplane designed mainly for speed is at maximum 

efficiency with given motive power efficiency. 

11. Name the requirements of airplane design for maximum velocity. 

12. State the reason why, with engine efficiency lowered, certain air¬ 

plane surfaces are at their best flying efficiency at high altitudes. 

13. What is meant by the minimum angle of incidence in flight? 

14. What flight quality is developed at low altitudes with optimum 

angle of incidence? 

15. State the effect on velocity at the angle of incidence for best climb. 

What will happen if the maximum angle is exceeded? J ) 



20 


Practical Aviation 


CHAPTER ANALYSIS 

Flight Stability and Control 

AIRPLANE EQUILIBRIUM: 

(a) Stability. 

(b) Longitudinal Stability. 

(c) Lateral Stability. 

(d) Directional Stability. 

(e) Center of Gravity. 

LONGITUDINAL STABILITY: 

(a) Lifting Surfaces. 

(b) Stabilizing Surfaces. 

(c) Longitudinal Dihedral. 

(d) Canard Principle. 

(e) Main Surface Dihedral. 

LATERAL STABILITY: 

( 

(a) Washout and Washin. 

(b) Ailerons. 

(c) Banking. 

CONTROLS: 

(a) Wheel and Column. 

(b) Joystick. 






CHAPTER III 


Flight Stability and Control 


Maintenance of airplane equilibrium is secured by (a) features of de¬ 
sign, (b) controls operated by the pilot. 

The following factors of stability and control are to be considered: 

(1) Stability —The natural tendency of a body disturbed to return to 
normal position. 

(2) Longitudinal Stability —The tendency of an airplane to maintain 
stability along the direction of normal horizontal flight and overcome pitching 
and tossing. 

(3) Lateral Stability —The tendency to oppose rolling sideways. 

(4) Directional Stability —The tendency to oppose swerving to the right 
or left of its proper course. 

In dealing with these factors, one must dispose of the popular miscon¬ 
ception that stability is fixed “steadiness” in flight, attained through skillful 
design. While not easily capsized, an inherently stable airplane does not 
respond readily to its controls; it is sensitive to all air disturbances and will 
roll and sway in response to air billows, whereas one of neutral stability 
answers its mechanical and automatic controls handily, and because it has 
no inherent tendency to hold a fixed position relative to the air, adjusts itself 
easily so that its position relative to the ground is not changed by air dis¬ 
turbances. 

It is well to remember that the air is at times treacherous and the air¬ 
plane should be so designed that it will sail through the medium on an even 
keel more or less of its own accord, yet not be too sensitive to air disturb¬ 
ances. Through actual participation in flight the aviator learns manipulation 
of controls according to the “feel” of the air, and this constitutes a large 
part of his training; it is at once seen, however, that this instinctive handling 
limits his usefulness unless with it goes an understanding of the principles 
of stability and control which govern flight. 

21 


22 


Practical Aviation 



CENTER OF GRAVITY 

The first consideration of airplane stability and general flying efficiency 
is the center of gravity, for the craft is suspended in the air and rotates about 
this point. The proper place for its location is where the forces of thrust, 
resistance, lift and weight act. 

Ordinarily, the airplane is so designed that the thrust line passes nearly 
through the center of resistance, and the center of gravity is made in line with 
the weight and lift. 

See Figure 14. 

The center of thrust is often placed below the center of resistance, for convenience. 
In pusher types the thrust is sometimes above the line of resistance. The tendency 
to nose down thus produced is overcome by having the center of lift back of the center 
of gravity. The principle of coincident centers is the factor of proper balance, but 
with variations in the position and strength of these forces produced in flight, the bal¬ 
ance is restored by small forces, such as the tail of the airplane. 

If the center of gravity is too low it produces a pendulum effect and 
causes a sideway roll of the airplane. When too high, if disturbed it seeks 
a position as far as possible from the original, tending to tip over the 
airplane. 

METHODS OF DETERMINING THE C. G. 

(a) Point of balance may be determined by placing a roller under the airplane. 

(b) The airplane swung from a point overhead and a plumb line dropped from 
this point. 

(c) With the machine supported at front and rear, the weight at each point de¬ 
termined and the distance between the two points measured. This is known as the 
method of moments. 





























Longitudinal Stability 


23 



LONGITUDINAL STABILITY 
LIFTING SURFACES 

Cambered wing surfaces are longitudinally unstable at angles of inci¬ 
dence below 12 degrees, at which angles fair lift-drift ratio is produced. 

In Figure 15, the centers of pressure of surfaces 1, 2 and 3 are indicated. 
The C. P. is the point at which all the air forces about balance. 

Surface 1 is cambered and in a position approximately vertical, moving in a direc¬ 
tion from right to left. Its center of pressure is along the exact center of the surface. 

With decrease in angle to one of about 30 degrees, the center of pressure moves for¬ 
ward to the position shown in Surface 2. 

In Surface 3 the angle of incidence has so decreased that there is a downward 
pressure at point A. Corresponding depressions in such negative angles increase pro¬ 
portionately the pressure A. The center of pressure being the resultant of all air forces, 
it is affected by the downward pressure at A and moves backward. This pushes up the 
rear of the surface and increases the tendency to dive. But as the surface’s angle of 
incidence is increased the pressure at point A decreases, whereupon the center of pres¬ 
sure moves forward and pushes up the front. If the angle is thus greatly increased the 
result is a “tail slide.” 

STABILIZING SURFACE 

Since the cambered wing surface is inherently unstable, a stabilizing 
surface at some distance in the rear, or at the tail, is added. This tail surface 
has less angle of incidence. 

Figures 16a, 16b and 16c illustrate the effect of the tail surfaces, the 
upper portions of the drawing showing main lifting surfaces at varying 
angles, and with tail attached in lower view. 

In Figure 16a, the lift force is in rear of the center of gravity, which tends to make 
the wing dive; in the lower view it is shown how the downward pressure on the tail 
counteracts this tendency. 

Figure 16b shows a surface with lift passing through the center of gravity. The 
wing is therefore balanced and tail pressure is not needed unless a sudden change in 
angle is effected. 

In Figure 16c the line of lift force is ahead of the center of gravity. The tendency 
of the wing to rear up is offset by upward pressure on the tail; note lower view. 


















24 


Practical Aviation 



LONGITUDINAL DIHEDRAL ANGLE 

The tail must have an angle of incidence smaller than that of the wings. 
The angle of incidence of the tail stabilizing surface is ordinarily about one- 
third of the aerofoil angle. The neutral lift lines of each, when projected 
to meet, make a dihedral angle. 

See Figure 17. 

Occasionally, the tail-plane’s angle is the same as that of the main lifting surfaces, 
the lessened angle of incidence required of the former being secured by the downward 
deflection of air from the upper aerofoil. 

To illustrate the effect of stability secured by the longitudinal dihedral, we may 
consider an airplane traveling a horizontal course; in this position the thrust and direc¬ 
tion of motion are identical. The nose of the machine then being suddenly deflected 
by some air disturbance, the angle of incidence is changed with the downward position. 
Assume that on the horizontal course the aerofoil angle was 12 degrees and with the 
deflection the thrust line is lowered, say, 3 degrees. The angle of incidence is not 
changed in the same proportion, because the momentum of the former (horizontal) 
course pulls it off the direction of thrust. 

The net change of angle of incidence will be assumed to be 2 degrees. Both main 
lifting surfaces and tail stabilizer are affected by the change because both are fixed 
to the airplane structure. Both have decreased, proportionately. The main lifting 
surfaces, with former angle of incidence at 12 degrees, have decreased to 10 degrees. 
The tail stabilizer, with former angle 0 degrees, has now a minus angle or negative of 
2 degrees. Therefore, since the main surfaces have lost 12 deg.—2 deg, or 1/6 of their 
lift, and the tail stabilizer is now at an entirely negative angle, the tail will fall faster 
than the main planes. The airplane in consequence rights itself, or readjusts to the 
former horizontal. 

The reverse happens when the nose of the machine is tilted up by a gust of wind. 
While both main lifting surfaces and tail surface increase angles of incidence in the 
same amount, the angle (which determines the lift) increases in greater proportion 
with the tail than with the main surfaces, which lifts the tail faster. The airplane then 
assumes its first position at a slightly greater altitude. 

The variation of angle of incidence is not as great as the variation of the airplane’s 
angle to the horizontal. 

Stability produced by the effect of the longitudinal dihedral exists only when there 
is momentum in the original direction. 

The stability adjustments described are taking place almost continuously in flight, 
although not always perceptible to the aviator. 
























Main Surface Dihedral 


25 



Figure 18 Figure 19 —Airplane of the Dunne type, with longitudinal dihedral 

surfaces 


CANARD PRINCIPLE 

In early types, such as shown in the lower left of the drawing on this 
page, Figure 18, it was customary to place the stabilizing surface in front. 
The tail-first principle possessed obvious disadvantages, notably that suffi¬ 
cient longitudinal stability could be had only by giving this a greater angle 
of incidence than the main lifting surfaces. Thus if the wings had an angle 
of 5 degrees, the forward stabilizer was set at an angle of incidence of 15 
degrees, which gave poor lift-drift ratio at high speeds. 

Low velocities were the rule in the early days and the defect in design 
was not appreciated until increased speeds were required. The principle of 
the forward stabilizer, known as the canard, is now obsolete. 

MAIN SURFACE DIHEDRAL 

Figure 19 shows a view of the Dunne airplane, from the right rear. This 
type has no stabilizing tail surface, longitudinal dihedral being given by the 
main surface having a decreasing angle of incidence toward the wing tips 
and corresponding camber. The theory is that the wing tips act as longi¬ 
tudinal stabilizers. 

This design has the following disadvantages: 

(a) Departure from the usual form of lifting surfaces, in plan a parallelo¬ 
gram, is a mechanical inferiority, requiring additional strength of construc¬ 
tion. This increases weight. 

(b) Aspect ratio is lowered because the leading edge of the aerofoil 
is not at a right angle to the direction of motion. Lift is lessened on account 
of lowered aspect. 

(c) Drift is increased by the action of the air on the V-shaped depression 
in the center of the aerofoil. This dip is pointed in the direction of motion 
and when the airplane is turned off its course to a direction which is the 
resultant of thrust and momentum, or a sideways motion, the air pressure on 
the corresponding side of the V depression turns the machine back on its 
course. It is obvious that the air reaction set up by this depression increases 

drift. 

(d) The necessity for decreasing the angle and camber toward wing 
tips increases time and cost of construction. 

ertical surfaces at the wing tips, as shown in the drawing, are some¬ 
times added, set at an angle producing the same stabilizing effect. Drift is 
increased by this arrangement, and efficiency lowered. 

































26 


Practical Aviation 


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Figure 20 Figure 21 Figure 22 

Lateral stabilizing effect of upwardly inclined wings 


LATERAL STABILITY 

Upward inclination of the lifting surfaces gives a degree of lateral sta¬ 
bility, the wings forming a dihedral angle. The tendency to a sideways roll- 
through air disturbance is thus corrected by the lower wing gaining greater 
pressure or lift and the consequent side slip restoring the machine to level 
position. 

In the upper portion of Figure 20 is a representation of a front view of an airplane 
in flight, lifting surfaces having equal horizontal equivalent. When the machine is tilted 
sideways, as shown in the lower view, the horizontal equivalent (H. E.) of the left 
wing, now horizontal, has increased; a decrease is seen in the right hand wing, the 
lower wing in consequence rising through its added lift. The airplane is thus restored 
to its first, or normal, position. 

The righting effect is not, however, proportional to the horizontal equivalents of both 
wings. In the upper portion of Figure 21 it is indicated that the reaction, when the airplane 
is at normal position, has a direction opposed to the gravity force, or weight, the two forces 
being evenly balanced, or equilibrium maintained. In the lower half of Figure 21, with the 
airplane tilted sideways the force of reaction is at an angle or not directly opposed to 
gravity force. The direction of motion is therefore no longer directly forward, the re¬ 
sultant of the thrust and momentum giving the added direction of motion indicated in 
the drawing. The airplane is thus moving sideways while flying forward. 

To be effective, the angle of the lateral dihedral must be great enough to force the 
airplane back to equilibrium, and overcome the tendency to turning caused by the in¬ 
creased air pressure exerted on the keel surface, greatest in effect toward the tail. 

The theory is advanced, and with some justification, that the lifting force is derived 
from the side-slip in the direction of the lower wing. Some designers therefore advo¬ 
cate for tractor biplanes a dihedral angle for the lower wing only. An increasing 
tendency toward this construction is noticeable. 

Figure 22 shows the side slip, with non-skid fins added where excessive 
dihedral is needed to balance large keel surface. 















































Washout and Washin 


27 



WASHOUT 

An airplane tends to turn over sideways in a direction opposite to that 
in which the propeller revolves. The adverse effect of propeller torque 
(drift) is neutralized by giving the wing tip on the s' le not affected a smaller 
angle of incidence. 

The washout is shown in Figure 23. 

Where practicable, the angle of incidence is also increased on the side 
tending to fall, its lift thereby being increased. Washin is the term used 
to describe the increased angle. 

Washing out the angle of incidence on both sides increases the drift, making pos¬ 
sible lessened angle for the ailerons (the lateral controlling surfaces shown in Figure 
24) which gives them better lift-drift ratio. 

AILERONS (WING FLAPS) 

In Figure 24, the drawing to the extreme right shows the smaller angle 
of incidence of the aerofoil (lifting surface) given by washout. In compar¬ 
ing it with the other aerofoil (top center of page) it is noted that the ailerons 
attached to both have the same inclination, although the ailerons 6f the aero¬ 
foil with washout have considerably less angle of incidence, therefore greater 
efficiency. 

BANKING 

When an airplane is turned off its course it does not instantly proceed 
along its new course. This is due to the momentum of the original course. 
The new direction is therefore the resultant of this momentum and the thrust, 
and the sideways skid caused by the centrifugal force turns the lifting sur¬ 
faces away from their proper horizontal position, causing lessened lift. Neu¬ 
tralization of this effect is created by “banking,” or tilting the airplane side¬ 
ways. 

With the angle of the lifting surface changed by banking, the inclination of bottom 
of the lifting surface makes the pressure or lift force a horizontal component of the 
centrifugal force. The velocity of the skid is that required to secure an air pressure 
or lift opposite and equal to the centrifugal force of the turn. The steepness of the 
bank is governed by the sharpness of the turn, increasing as the strength of the centri¬ 
fugal force. 

It is obvious that when banking the entire lift force is no longer vertical, 
and it is important that it be sufficient to support the weight of the airplane, 
or it will fall. Speed is a requirement to offset this. 

Pilots mast not try to climb while banking. 

Slight banking results in skidding, which is easily corrected. 

Too steep banking, however, may result in a side slip inward, which is likely 
to be followed by a nose dive. 

























28 


Practical Aviation 



(c) Committee on Public Information 






























Dep Control and Joy Stick 


29 



DEP CONTROL 

The illustration above shows the airplane’s mechanical means of directional and 
lateral control. These comprise operation of the elevators, ailerons (sometimes called 
“wing flaps,” when attached to main lifting surfaces as shown in drawing), and the 
rudder. 

All operate on the principle of air force derived from an inclined plane. 

The elevators are controlled, in U. S. training machines, from the column which 
supports the wheel, as shown. 

The ailerons, or wing flaps, for lateral control are moved by the wheel in the 
cockpit. 

The rudder is controlled by a foot bar. 

The elevators are inclined up or down to depress or lift the tail of the airplane. 

The ailerons supply the difference in angle to the two tips of the wings, as 
needed, causing one to lift more than the other. 

The rudder’s action in turning the machine is due to the varying wind pressure 
exerted on the sides when moved to one side or the other. 

JOY STICK 

Figure 25b, at the bottom of the page, shows the stick control usually preferred 
for speed work, and widely known to aviators as the “joy stick.” Pushing the stick 
sideways toward a wing tip raises its aileron (wing flap) and deflects the aileron on 
the opposite end. When the stick is pulled back the elevators at the tail are raised, 
and when pushed forward they are dropped. 




















































30 


Practical Aviation 


REVIEW QUIZ 

Flight Stability and Control 


1. Classify and define stability as it applies to airplane equilibriurr 

2. What undesirable qualities has an inherently stable airplane? 

3. State the proper location for an airplane’s center of gravity. 

4. What is the effect if the center of gravity is too high? If too low? 

5. How is the point of balance determined? 

6. Below what angle are cambered surfaces longitudinally unstable? 

7. Why is the tail stabilizer necessary? 

8. Explain the action of the tail surfaces. 

9. What is the relation of the tail’s angle of incidence to that of 

the wing? 

10. When is the stability produced by longitudinal dihedral effective? 

11. By example, illustrate the effect of stability secured by the longi¬ 

tudinal dihedral. 

12. Why was the canard, or tail-first construction, discarded? 

13. Explain how the Dunne machine omitted the tail stabilizer and 

state the disadvantages of this type of construction. 

14. Explain the stabilizing action of a lateral dihedral. 

15. Why is washout applied to wing tips? 

16. Is the angle of incidence of ailerons affected by washout? 

17. State the reason why the airplane is “banked” when turned off 

its course. 

18. Why is steep banking dangerous? 

19. Define in detail the mechanical means for operating directional and 

lateral control surfaces by foot bar, wheel and column. 

20. What is the operation of the “joy stick”? 



L ead/ng edge. Mng support .. Centra/ p/one tra/t/ng edge 


Airplane Fuselage 


31 



General view of an airplane with fuselage covering removed, showing details of body construction 

















































































































32 


Practical Aviation 


CHAPTER ANALYSIS 

Materials, Stresses and Strains 

ACTION ON MATERIALS: 

(a) Stress. 

(b) Strain. 

(c) Factor of Safety. 

STRESS AND STRAIN FORCES: 

(a) Compression. 

(b) Tension. 

(c) Bending. 

(d) Shearing. 

(e) Torsion. 

STRENGTH OF WOOD UNDER STRESS 


(a) 

Straightness. 

(b) 

Fit. 

(c) 

Condition. 

WOOD 

FOR AIRPLANES: 

(a) 

Spruce. 

(b) 

Ash. 

(c) 

Maple. 

(d) 

Hard Pine. 

(e) 

Walnut and Mahogany. 

(0 

Cedar. 

(g) 

Hickory. 

WING 

COVERING: 

(a) 

Fabric. 

(b) 

Dope. 


METAL FITTINGS AND WIRE: 

(a) Steel. 

(b) Other Metals. 

(c) Wire. 





I 


CHAPTER IV 

Materials, Stresses and Strains 


The student having now mastered the theory of flight and the funda¬ 
mentals of design of airplane lifting surfaces and controls, knowledge of 
rigging is next in order. 

As an infantryman’s first care is for his feet, and a cavalryman for his 
mount, so must the military aviator know his means of locomotion, his air¬ 
plane. The army does not require the dismounted soldier to be a chiropodist, 
or the cavalryman a veterinarian, no more than the aviator is expected to 
be an expert mechanic. But he must know whether or not his machine is 
in condition, and what he may expect of it, without recourse to another’s 
judgment. With the engine out of order a safe landing can be made, but 
when something goes wrong with the rigging there is trouble ahead. Should 
the rigging be wrong, even though nothing breaks, speed is lessened and 
stability and control made less effective. 

Rigging an airplane properly presupposes knowledge of the stresses it 
is subjected to and the strains which may appear. Airplane materials are 
of the size and weight which combine greatest strength and least weight. A 
knowledge of them is important. 

Stress is the load which a body bears. It is generally expressed thus: 
L - 4 - A = S, where L is the load, A the square inches contained in the cross- 
sectional area, and S the resultant stress. For example, with an object meas¬ 
uring in cross-section 3" X 2" (an area of 6 sq. in.) and required to support 
a total load of 12 tons, the stress would be 12 6 = 2 tons. 

Strain is deformation produced by stress. 

If a spar is known to collapse under a maximum stress of 1200 lbs., in a 
training machine it would be subjected to no greater stress than 100 lbs.; thus 
where known stress of an object is 1200 lbs., and the maximum stress it is 
called upon to endure is 100 lbs., then 1200 lbs. -f- 100 lbs. = 12, representing: 

The Factor of Safety, which is ordinarily expressed by the resultant of 
known collapsing strength divided by maximum stress the object is called 
upon to endure. 


33 


34 


Practical Aviation 



Figure 26 —Compression and tension stresses Figure 27 —An illustration 

produced by wood bending of shearing 


STRESS AND STRAIN FORCES 

Strength of materials must be understood from the viewpoint of strength 
in compression, tension, bending, torsion and shearing. For example, wire 
is designed to take tension but not compression, wood takes compression but 
not shearing, bolts are liable to shearing, etc. 

Compression—The stress of pressure produces a crushing strain, best exampled 
by the stress on interplane struts. 

Tension—The stress of pull, tending to elongation, exampled by all wires. 

Bending—A combination of tension and compression exampled by the bending of 
wood, the outside fibres tending to pull apart, the inside to go together. 

Shearing—A cutting off sideways by a pull such as is exerted on an eyebolt or pin. 

Torsion—A twisting stress, a combination of the forces of compression, tension 
and shearing, such as is received by the propeller shaft. 

Bending —Figure 26 illustrates how the combination of compression and 
tension stresses are produced by bending. The upper view shows a straight 
piece of wood, the top line (A), the center line, or “neutral axis” (C) and the 
bottom line ( B ) being all of equal length. In the lower view the same piece 
of wood is bent. Then center line (C) is still the same length, but the top 
line (A) is further from the center and therefore longer. This is due to the 
stress of tension producing the strain of elongation; the upper portion is 
therefore in tension, which increases with its distance from the center. Mean¬ 
while, the bottom line, under the strain of crushing produced by the stress of 
compression, has become shorter than the center line. At the center line, 
therefore, there is neither tension nor compression and the wood nearest the 
center is under considerably less stress than that near the top and bottom 
lines. Thus the center may be hollowed out without appreciably weakening 
the wood, which makes it possible to save about 25 per cent, of the weight 
of the wood used in the construction of an airplane. 

Shearing —In Figure 27 a wire exerting pull on an eyebolt is shown. 
The lower view illustrates how the stress may shear an eyebolt. 





































Strength of Wood 


35 



STRENGTH OF WOOD UNDER STRESS 

Upon the care exercised to have struts kept perfectly straight and evenly 
bedded into sockets rests the strength of wood under compression. A stick 
1 inch in diameter and 36 inches long, if kept perfectly straight can perhaps 
bear a ton weight without breaking, but if it were not straight, or had started 
to bend, a compression of 50 pounds would break it. Weight being of the 
greatest importance in airplane design, the wooden parts are kept as far as 
possible in direct compression. To save weight is the aim of all designers 
and in consequence an airplane’s factor of safety is ordinarily low. The 
required stresses for parts in direct compression may be safely taken, how¬ 
ever, if they meet the requirements which follow: 

Straightness —Spars and struts must be perfectly straight. Viewed in cross-sec¬ 
tion, these supporting members are elliptical in shape (stream lined); the center of 
strength is therefore midway between the points of greatest transverse width. If the 
stress of compression is not equally distributed about this point the strut will bend, 
because tension will be created on one side and compression on the other. The effect 
of a strut bending is shown in Figures 28-a and 28-b. In the former the wire stays are 
taut and the proper gap between wings maintained. With the strut bent, as in Figure 
28-b, the gap is lessened and the wires have become slack, efficiency in flight being there¬ 
by lessened. 

Fit —Struts and spars must fit their sockets accurately and be bedded correctly. 
While snugness is essential, the wooden portions of the structure must slide into their 
sockets or fittings by pushing; a hammer is" never required. The bottom should fit the 
socket exactly. In Figure 29, strut A is correctly bedded; strut B is not snug at the 
bottom, in consequence of which the compression stress is not evenly distributed about 
the center of strength and a bending stress is produced. 

In assembly, the customary test consists of painting the bottom of struts before they are fitted to sockets; 
the paint must be distributed over the entire bed when strut is withdrawn. 

Condition —Struts and spars must be undamaged. If the wood is scored or dented, 
and the strut or spar should be subjected to a bending stress, the outside fibres receive 
the greatest strain (as explained on the preceding page) and the collapse will come at 
the imperfect point. Cross grain, knots and similar blemishes are prohibited for the 
same reason. 

The wood must also be well varnished to keep the moisture out. Variation in the 
dampness of the atmosphere causes wood to expand and contract, the danger in this 
variation being that this expansion and contraction is not evenly distributed and the 
symmetry of the spar or strut is lost. 






































36 


Practical Aviation 


WOOD FOR AIRPLANES 

Practically all of the airplane’s framing is constructed of wood, one 
reason for this being that flaws can easily be detected; consequently, wooden 
parts are seldom painted, preservation being secured by the use of varnish 
which brings out clearly any defects. Lightness, strength and rigidity are 
the prime requirements for flying machine construction. Certain woods best 
fulfill these, better in fact than any metal. This may be illustrated by a com¬ 
parison of spruce with aluminum, lightest of the metals. 

A cubic foot of spruce weighs 27 pounds. 

A cubic foot of aluminum weighs 162 pounds. 

Tensile strength of spruce per square inch is 7,900 pounds. 

Tensile strength of aluminum per square inch is 15,000 pounds. 

Compression strength of spruce per square inch is 4,300 pounds. 

Compression strength of aluminum per square inch is 12,000 pounds. 

On the cubic foot basis, the weight of spruce has a decided advantage 
over metal. Aluminum’s weight is 6 times greater; brass about 19 times 
greater; nickel and steel about 18 times; copper about 20 times. 

While wood is not as strong as steel of the same size, the construction 
of struts requires a certain thickness in proportion to their unsupported 
length, so the use of spruce, although it offers by its size more head resist¬ 
ance, is to be preferred because strength against bending is secured with less 
weight. 

Preferential woods for airplane work are Spruce, Ash, Pine, Maple, Wal¬ 
nut, Mahogany, Cedar and Hickory. The selection of the right kind of 
lumber is largely a matter of experience, but the fundamentals are soon ac¬ 
quired with application to the subject. 

Spruce —The strongest and most generally satisfactory material when clear grained, 
straight, smooth and free of knot holes and sap pockets. Combining flexibility, light¬ 
ness and strength, it is used for struts and spars. 

Ash —A straight-grained wood, strong in tension, springy, but heavier than spruce. 
It is used for main spars, longerons, engine supports, rudder post, etc. 

Maple —A strong wood suitable for small parts such as the blocks to connect rib 
pieces across a spar. 

Hard Pine —A tough and uniform wood adapted for the long braces in the wings. 

Walnut and Mahogany —Uniformity, hardness and finishing qualities are the 
reasons for extensive use of these woods for propellers. 

Cedar —Lightness, uniformity and easy working qualities recommend this wood 
for occasional use in fuselage covering. Three-ply wood, or veneers, are sometimes used. 

Hickory— Tough, hard and springy, this is the favored material for skids and 
landing chassis struts. 

Condensed Table of Weight and Strength 
U. S. Government Specifications 


Wood 

Weight per cubic 
foot (15% 
moisture) 

Modulus of rupture, 
pounds per square 
inch 

Compression 
strength, pounds 
per square inch 

Hickory. 

50 

16,300 

7.300 

Ash. 

40 

12.700 

6,000 

Walnut. 

38 

11,900 

6,100 

Spruce . 

27 

7.900 

4.300 


Linen and cord are used for wrapping wooden members to increase 
strength against splitting; the winding is made very tight and treated with 
"‘dope” or glue for waterproofing and also to increase the tightness. Wooden 
parts are ordinarily ferruled at the ends, usually with copper or tin, to pre¬ 
vent the bolt pulling out with the grain, to prevent splitting and to supply 
a uniform base. 

























Wing Covering and Dope 


37 



Figure 30 —View of wing surface and method of applying covering 


WING COVERING 

Unbleached Irish linen, stretched rather loosely on the frame of the wing 
and then treated with “dope,” is the almost universal covering for airplane 
lifting surfaces. 

This fabric is woven with the “warp” of the yarn lengthwise and the 
“weft” across the cloth. It tests to a 60-pound tension on an inch-wide strip, 
and when doped shows a strength of at least 70 pounds per inch. It ordi¬ 
narily weighs 3*4 to ounces per square yard. Doped and finished, air¬ 
plane linen weighs about 0.10 pound per square foot, inclusive of tape and 
varnish for both top and bottom faces of the surface. 

Rubberized fabrics, formerly used, were discarded because of the necessity for 
stretching them tightly by hand on the frame, and because they tightened in dampness 
and sagged in dry weather. 

The strips of the linen wing covering are sewed together by machine, 
forming a bag which slips easily over the framework, seams running diago¬ 
nally across the wing. Figure 30 illustrates a partial covering on the wing 
framework. 

A cotton fabric, the new way of spinning which is a closely guarded military secret, 
has been added to the materials for wing covering. Under the most rigid tests it sur¬ 
passed in strength the stoutest linen. 

DOPE 

Dopes for coating linen wing coverings are of several kinds, but all are 
some compound of cellulose acetate or nitrate, soluble in ether or in aceton. 
Through doping, the linen is tightened up on the frame and given a smooth, 
weather-resisting finish. 

The United States Army requires four coats of nitrate dope, this cover¬ 
ing being varnished with two coats of spar varnish after the dope has set; 
this acts as waterproofing and protects the dope from peeling. Doped fabrics 
are best cleaned by soap and water. 

Trade names of commercial dopes include: Cellon, Novavia, Emaillite, Cavaro and 
Titanine. 




38 


Practical Aviation 


METAL FITTINGS AND WIRE 

STEEL 

Chrome nickel or vanadium steel, specially heat-treated, is often used for 
bolts, turnbuckles and pins. When parts are to be bent, special care must be 
taken that the heating is not done unequally. Serious weakening may result. 

Cold rolled steel, used largely for ferrules, clips and fittings in airplane 
construction, is harder than mild annealed steel, works easily and wears well. 
Its grain is well marked and it should be remembered that it is weakest 
across the grain. Sharp bends should never be made and, unless one is fa¬ 
miliar with annealing, any required bend should be made slowly in a vise. 
The j aws of the vise should be protected by thick copper pads to prevent 
nicking the plate. 


OTHER METALS 

Copper and tin are used for tanks and ferrules of wire joints. 

Where rust resisting qualities are essential on metal fittings, “monel metal is 
extensively used. It is composed of 60 per cent nickel, 35 per cent copper and 5 per cent iron. 
Aluminum is unreliable and is never used in important fittings. 


CRYSTALLIZATION AND FATIGUE 

Metal is subject to crystallization and fatigue. 

Crystallization —Constant vibration and jarring which causes easy break¬ 
age at a particular point. 

Fatigue —Repeated strains of bending and twisting result in loss of 
“springiness” of metal, lessening its strength. This is known as fatigue. 


WIRE 

Two types of wire are used on airplanes: solid-drawn, for all minor 
bracing purposes; flexible cable, for control, flying and landing wires. 

Aviation wire —This is a single wire, piano grade. While it is the strongest for its 
weight, it forms kinks easily when coiled and may be seriously injured by a blow. Its 
main use, therefore, is for braces in the protected fuselage and wings. 

Aviator strand —This is 7 or 19 wires stranded together and used for tension wires 
because of its elasticity, permitting it to be bent around parts of small diameter. 

Tinned aviator cord —This is a cord or rope stay, composed of seven strands of 7 
or 19 wires twisted into a rope. The wires are galvanized as a protection against rust, 
but where the heat required for galvanizing will injure hard or small wires, they are 
tinned. It is in general use for controls, and although less strong as the same size 
in single wire, has the advantage of not being seriously injured by a single weak spot. 





Practical Aviation 


39 


REVIEW QUIZ 

Materials, Stresses and Strains 


1. Why is a knowledge of strength of materials valuable to the 

aviator? 

2. Define stress and give an example with an object of definite area 

supporting a given weight. 

3. What is strain? 

4. By an example, explain the factor of safety. 

5. Briefly state the difference between the forces of compression, ten¬ 

sion, bending, shearing and torsion. 

6. How is it possible to hollow out wooden parts without appreciable 

weakening? 

7. State the value of direct compression upon struts. 

8. Give the reason for the care exercised in keeping struts straight. 

9. How should a strut be bedded? 

10. Why is it important that struts or spars should not be scored or 

dented? 

11. Of what value is varnish? 

12. In what respects is spruce superior to aluminum for airplane 

framing? 

13. Explain how wooden members are given increased strength against 

splitting. 

14. What material is generally used for wing covering? 

15. How is the covering made and placed on the framework? 

16. What is the purpose of dope and what is its composition? 

17. Give some commercial names of dope. 

18. In bending chrome nickel or vanadium steel what caution should 

be exercised? Cold rolled steel? 

19. Define crystallization and fatigue. 

20. State the composition and uses of aviation wire, aviator strand, 

tinned aviator cord. 







40 


Practical Aviation 


CHAPTER ANALYSIS 


Rigging the Airplane 


ERECTION AND ASSEMBLY: 

(a) Landing Gear. 

(b) Horizontal Stabilizer. 

(c) Vertical Stabilizer. 

(d) Rudder. 

(e) Elevators. 

ASSEMBLY OF LIFTING SURFACES 

(a) Center Section. 

(b) Main Wing Section. 

(c) Assembly. 

ALIGNMENT: 

(a) Landing Gear. 

(b) Wings Without Stagger. 

(c) Staggered Wings. 

(d) Main W ing Sections. 

(e) Dihedral Angle. 

(f) Angle of Incidence. 

(g) Droop. 

(h) Controlling Surfaces. 

(i) Over-All Adjustments. 

CONTROL CABLES AND WIRES: 

(a) Adjustment of Controls. 

(b) Turnbuckles. 

(c) Cables. 

(d) Wire Loops. 

(e) Tightening Wires. 

EFFECT OF ALIGNMENT ERRORS: 

(a) Directional Stability. 

(b) Lateral Instability. 

(c) Longitudinal Instability. 

FLIGHT DEFECTS: 

(a) Poor Climb. 

(b) Lessened Speed. 

(c) Poor Control. 

(d) Uncontrollable on Ground. 






CHAPTER V 


Rigging the Airplane 


With a thorough understanding of the fundamental factors that make 
for flight efficiency, practical rigging of the machine may be turned to in full 
confidence of doing a good job. Reasonable familiarity with the use of simple 
tools remains to be acquired; but this is a short process of practice in their 
handling, the keystone of success being the exercise of care. If the prelimi¬ 
nary study has been conscientious up to this point, the reason for each step 
in assembly will be clear without explanation and the requisite exactness 
will follow as a matter of course. 

Golden Rules of Rigging 

Don’t hurry. If the job is a rush one, make haste slowly. 

Never lay tools on the planes. 

Pliers or wrenches are not for use on airplane bolts; a burred thread, 
or one damaged in any way, should be discarded. 

Turnbuckles are to be started from both ends. 

There should be a cotter pin for every nut and safety wires should lock 
all pins and turnbuckles. 

Wire with a kink in it should be brought to the attention of some one 
in authority. 

Don’t hammer or pound bolts and pins into position; they must go into 
place by pushing or gentle tapping. 



(c) Committee on Public Information 

Figure 31 —Assembling and rigging U. S, Army airplanes at a dying Held 

41 















42 


Practical Aviation 



Figure 32a—Method of attaching land- Figure 32b—Method of attaching horizon 
ing gear tal stabilizer 


ERECTION AND ASSEMBLY 

An assembled airplane is a trim and fairly hardy machine, but before 
assembly the parts are fragile. When received, the greatest care should be 
exercised in unpacking boxes and crates. 

The order of assembly and directions follow: 

Landing Gear—Mount the wheels on the axle and bolt them into place. 
Connect up the tail skid by pinning the front end to the spring fitting and 
the other end to the socket of the tail post. Now raise the fuselage to receive 
the landing gear. This may be accomplished by blocking, or by tackle as 
shown in Figure 32a, where a line is passed under the sills of the engine bed 
—nowhere else—and caught by the hook of the hoisting block. Raise the 
front end of the fuselage until the lower clips of the longeron line up with 
the clips on the ends of the landing gear struts. The bolts are then passed 
through the aligned holes and the nuts drawn up tight. Cotter-pins are in¬ 
serted in the holes drilled through the bolt, which then appear just beyond 
the castle of the nut. The leaves of the cotter-pins are turned backward, > 
locking the nuts in place. The gear should then be aligned in accordance with 
instructions on page 44. 

Horizontal Stabilizer—With the landing gear attached to the fuselage, 
elevate the tail of the machine, supporting it on a horse of proper height, or 

block until the upper longeron is level, verifying the arrangement by use of 

a spirit level placed on the upper longeron at the tail. See Figure 32b. Bolt 
the horizontal stabilizer to the top longeron and tail post and draw all nuts 
tight and secure them with cotter-pins. 

Vertical Stabilizer—Fasten the vertical stabilizer by bolting it through 
the forward part of the horizontal stabilizer and the clip at the front of the 
vertical stabilizer; tighten nuts and lock with cotter-pins. A double clip in 
the rear passes over the two bolts which fasten the horizontal stabilizer to 
the tail post. Attach the flexible wire cables and tighten by the turnbuckles. 

Rudder—Attach the control braces so that the upper tips point toward 
the line of the hinge. Mount the rudder on the tail post and vertical stabil¬ 
izer and insert the pins in the hinges, securing them with cotter-pins. 

Elevators—Attach the control braces in the same manner as with the 
rudder and mount the elevators on the horizontal stabilizer by means of the 
hinges and pins, the latter being secured by insertion of cotter-pins in the 
holes drilled for that purpose. 


















43 



Figure 34 —Curtiss strut numbering 


Figure 33 —Assembly of center section 


B - bra any/ /vires 
F~ f/ying /vires 
L * landing wires 


Figure 35 —Method of wiring 


Assembly of Lifting Surfaces 


(c) Committee on Public Information 


—-f . 7 


ASSEMBLY OF LIFTING SURFACES 

Center Section—The section of wing surface first attached is that which 
is directly over the fuselage and known as the engine section panel. With 
the struts fitted into the proper sockets of the wing surface, the entire section 
with bracing wires attached, is lifted and set into the sockets on the upper 
longeron. Bracing wires are then attached and the section aligned. 

The method is clearly shown in the photograph, Figure 33. 

Main Wing Sections—While the upper lifting surfaces may be first as¬ 
sembled to the engine section and the lower wing then attached, it is prefer¬ 
able to complete assembly of the sections, or panels, before attaching them 
to the fuselage. The advantage of the latter method is that less adjustment 
is required and the correct stagger and dihedral is secured. 

Figure 34 shows the numbering of struts on the Curtiss JN-4. These 
may be quickly committed to memory by noting that the four struts of the 
center, or engine section panel, are not designated, and that beginning at the 
left from the pilot’s seat, the eight remaining struts are numbered from 1 to 8. 

The main struts bear a number and can easily be read from the pilot’s seat; it is 
therefore at once evident if, through error, a strut is inverted. 

Assembly—The upper wing of the left lifting surface receives struts Nos. 
1 and 2 in the proper sockets. The wires are then connected to right and left 
by clips and adjusted by turnbuckle until the spars are straight. The wing is 
then set on a cushioned block, leading edge down. See Figure 31. 

The lower left wing is then brought, leading edge resting on cushioned 
block, to a space equal to the length of the struts. Diagonal wires are loosely 
connected and spars inserted in sockets, 5 and 6, and bolted into place. 

The “landing,” or single, wires and the “flying,” or double, wires of struts 
1 and 5 are then connected closely, so the wings may be held together while 
being attached to the fuselage. 

Figure 35 clearly indicates the wiring of the assembled airplane wings. 

The erection of the wing must be done with special care. Lifting by the 
struts or edges of the wings may result in a serious strain. Boards placed 
under the beams of the wing framework should be used for carrying. 


















44 


Practical Aviation 



Figure 37a Figure 37b—Stagger alignment 


ALIGNING THE AIRPLANE 

Correct alignment of an airplane is of tremendous importance. Its flying 
efficiency depends largely upon exactness in truing up all controls and wires 
and securing proper angle of incidence and dihedral. The parts should be 
aligned in regular order as follows: 

Landing Gear—To be aligned before wings are attached to fuselage. The axle should be parallel 
with the lateral axis of the fuselage. Ascertain the exact center of the fuselage and the axle; with spirit 
level align the cross width of the fuselage. Drop a plumb line from the center of the fuselage and adjust 
the cross wires until it is in the exact center of the axle. 

Or, if plumb bob and line are not available, adjust the cross wires so that the measurement A-B is 
exactly equal to the measurement C-D in Figure 36. The adjustment is made on both front and rear sup¬ 
ports of the under carriage. 

The landing gear and fuselage are aligned in the factory, but their correctness should be determined 
by the method just given. Before aligning, it is well to verify that the tail support still holds the fuselage 
horizontal. 

Center Section—The bracing wires (A-B, C-D, Figure 37a) are left sufficiently tightened to keep the 
struts straight, while the wings are being aligned. 

Without Stagger—The upper longerons of the fuselage being horizontal, the struts are properly 
placed when they form a right angle. Adjust the sides first and then the front. Check the perpendicular 
alignment by measuring off an equal distance on the upper longeron back and forward of some point on 
the bottom of the strut; the strut will be exactly perpendicular when the distance from these two points to 
the top of the strut measures exactly the same. Tighten bracing wires evenly until sides and front are cor¬ 
rectly aligned; i. e., until the measurement of corresponding points on cross wires are identical. 

Staggered—The angle of strut fittings and sockets serves as a guide to the degree of stagger. The 
airplane’s specifications state the stagger; for example in the Curtiss JN-4 it is 105/6 inches. This is 
checked by a plumb line suspended from the leading edge of the top surface, as in Figure 37b, and the 
measurement is taken between points A-B; that is, the plumb line should be 10^6 inches in advance of the 
leading edge of the lower wing. 

In all types of airplanes the specifications state how the measurements should be taken (a) along the 
line of the chord, or (b) horizontally. 

When the stagger is verified, the wires should be tightened and the cross distances measured until one 
side corresponds exactly with the other. Side wires should be adjusted first, and then the front, and cross 
distances measured until they correspond exactly. 

Main Wing Sections—The first point to determine is whether leading edges of the upper and lower 
wing surfaces are exactly in line with the center section. Standing on a step ladder, 15 feet to one side, 
a sight by eye is taken along the leading edge of the upper plane. If not straight, the adjustment for warp 
or bow is made by tightening or loosening the front landing wires. The same should then be done for the 
lower plane and the opposite wing aligned in the same manner. When the cross wire adjustments have 
been completed, a sight taken from both ends of the wings should show all struts in line and parallel with 
the center section struts. 






























Aligning the Airplane 


45 



DIHEDRAL ANGLE 

One method of securing the dihedral angle is shown in Figure 38, where Ta is a tack 
placed in the exact center of the center section, on the leading edge of the upper wing. The 
exact distance is measured off then on each side and tacks, Tb, Tc, placed in the leading edge 
of both upper wings, at a point near their tips. A string is stretched tightly between Tb and 
Tc. The specifications are then referred to and the dihedral angle checked. Assuming the 
dihedral angle to be 176 degrees, then each wing has been raised 2 degrees. The natural 
sine of 2° being 0.0349, this, multiplied by the distance between Tb and Ta (or Ta and Tc) 
gives the proper distance between Ta and the string directly above it. 

Example: 

The distance Tb-Ta (or Ta-Tc) is 16 feet=192 inches. 

192 in.X0.0349=6.7 in., or the proper distance between Ta and the string above, if 

wings are set at the proper dihedral. 

In making the alignment, wings should be raised equally until the correct measurement 
over the center section is secured, with leading edges kept straight. 

All adjustments should be made by altering the wires from the inside bays; when 
diagonal wires are to be tightened make sure that the opposite wires in the same bay 
are slackened off. 

Check up the alignment by measuring (Figure 38) from Ta successively to points D, B, 
C, E, making, certain that the distance Ta-B corresponds with Ta-C, and Ta-D is the same 
as Ta-E. This will show that both wings are the same height. 

ANGLE OF INCIDENCE 

The specifications give a set measurement for the angle of incidence. Verify the 
horizontal position of the top longeron of the fuselage, i. e., make certain that the air¬ 
plane is in flying position. Then place the straight-edge underneath the center of a 
rear strut as shown in Figure 39. With a spirit-level, adjust the straight-edge to hori¬ 
zontal position. Refer to the specifications and note the set measurement given; this 
will require measurement from 

(a) —the lowest part of the leading edge to top of the straight-edge, or 

(b) —the center of the front strut to the top of the straight-edge. 

This measurement must be repeated under every strut, or the lower surface where 
struts occur. 

The measurement should not be made between struts, because the wings may be 
slightly warped. 

If the angle is too great; 

Slacken all the wires attached to the top of the rear strut and tighten all the 

wires attached to the bottom. 

If the angle is too small: 

Slacken all wires attached to the bottom of the strut and tighten all wires 

attached to the top. 

The correct adjustment, laid down in the specifications, should be made with no 
greater variation than 1-16 inch. The measurements at all struts must agree, i. e., the 
angle of incidence all along the wing must be the same, unless the wings have a wash¬ 
out or washin. 

Check up the stagger with a plumb line to see that it ha$ not been disturbed while 
securing the dihedral. 
















■4 


46 


Practical Aviation 



DROOP 

When the angle of incidence and the stagger have been adjusted, one 
wing must be slightly drooped to correct for the torque of the propeller, where 
a single propeller is used in tractor airplanes. 

With a propeller that turns to the right (clockwise) the left wing is drooped. If it 
turns to the left the right wing is drooped. 

For machines up to 100 horsepower, the outer rear landing wire of the 
wing which is to be drooped is slackened until the trailing edge between outer 
and intermediate struts is about 1 inch lower than the rest of the trailing edge. 

CONTROLLING SURFACES 

Since the pilot depends upon the manipulation of controlling surfaces to' 
manage his airplane, exceptional care should be taken that ailerons, eleva¬ 
tor and rudder are properly rigged. 

Ailerons, Trailing Edge (wing flaps)—With the control levers rigidly blocked into 
neutral position, the aileron should be rigged so its trailing edge is about 24 inch below 
the trailing edge of the surface to which it is attached. In flight the angle of incidence 
of the surface will cause it to lift a little above the position, or to the true line. This 
is illustrated in Figure 40 where the dotted outline shows the position during flight. 

A basis of measurement commonly used is *4 inch depression for every 18 inches of 
chord of the controlling surface. 

Tail Stabilizer—With the weight of the tail supported by the tail skid, align the 
rear edge of the stabilizer so it is straight and parallel with the lateral axis of the air¬ 
plane. Take a sight from the rear to the leading edge of the upper plane, which 
should be in alignment with the trailing edge of the stabilizer. Tighten the wires by 
turnbuckles. 

Elevator Flaps—With the controls in neutral position adjust the control wires by 
turnbuckles until the elevator flaps are in the same plane, and sufficiently tight to 
eliminate lost motion. 

Rudder—Adjust the control wires by turnbuckle until both foot bar and rudder in 
neutral position show no lost motion in control. 

Over-All Adjustments—Figure 41 illustrates the measurements which are taken 
as a final check. The measurement A-B must equal A-C within % inch. Point A 
is the center of the propeller (in pusher types, the center of the nacelle) and B and C 
are points marked on the outer spars equally distant from the butts of the spars. 
The measurement should be taken from both top and bottom on each side. 

D-F should equal E-F within % inch. The rudder post is point F , and D and E 
are points on the rear struts marked as in the case of B and C. Two measurements, 
top and bottom, are also taken here. 

























Adjustment of Control Cables and Wires 


47 



CONTROL CABLES AND WIRES 

Adjustment of Controls—From the pilot’s seat move the control levers 
and note if a quick movement shows lag or snatch in the movement of the 
control surfaces. Movement of inch to either side should produce corre¬ 
sponding motion of the controlling surfaces. 

Turnbuckles—The turnbuckle, which is shown in Figure 42a, is a barrel 
with an eye-bolt screwed into each end; it is therefore hollow and should not 
be turned with pliers. It is best adjusted by passing a piece of wire through 
the hole in the center and using it as a lever. The illustration shows the 
proper method of using the locking wire, so the barrel may not turn and 
thereby throw the airplane wires out of the fine adjustments required. 

Cables—Windings must be even with a stream-lined effect at the end 
of the winding as shown in Figure 42b. The dimensions of the winding 
before it tapers off (see A, in the illustration) must be at least 15 times as 
great as Z), the diameter of the cable. Only non-acid flux should be used in 
soldering. 

Correct Winding for Cables 



Length of 

Breaking 


Length of 

Breaking 

Size of Cable 

Winding 

Strength 

Size of Cable 

Winding 

Strength 

Inches 

Inches 

Pounds 

Inches 

Inches 

Pounds 

1-32 

\ x A 

185 

5-32 

23/4 

3,200 

1-16 

l y 2 

500 

3-16 

3 

5,500* 

3-32 

114 

1,100 

7-32 

344 

6,100 

7-64 

iy 4 

1,600 


3-/s 

8,000 


2 

2,100 

5-16 

434 

12,500 


*For cable; loop strength is 5,100 pounds. 


Control cables wear and fray out by friction with pulleys; careful exam¬ 
ination should be made after each flight, and if a single strand is broken 
the cable should be replaced. 

WIRE LOOPS . , . . . , . . 

Wherever a loop is made with wire to connect with a fitting or turn-buckle it 
should be symmetrical in shape and reasonably small, with well defined shoulders. A 
loop properly made is shown at the left of Figure 42c, and one improperly made at 
the right. Where the shoulder is not properly made and the loop elongated the 
ferrule is likely to slip up and throw the wire out of adjustment. 

When the loop is finished the wire should be undamaged. Wire bent to the degree 
shown at the lower end of Figure 42c should be discarded. 

TIGHTENING WIRES . , 

Care must be exercised that wires are not too tight or extra loads wifi be placed 
on spars and struts. Wires should never be at a tension so they sing. 







































































48 


Practical Aviation 


THE EFFECT IN FLIGHT OF ALIGNMENT ERRORS 
DIRECTIONAL STABILITY 

Wrong Angle of Incidence —The airplane will turn toward one side if 
the angle of incidence of one side of the wing surface or tail surface is wrong; 
for drift increases with greater angle and decreases with lessened angle. 

Fuselage, Rudder-fin or Struts Off Line of Direction of Flight —The air¬ 
plane will turn off its course, for unless these are aligned they will act as a 
rudder. 

Distorted Surfaces —The airplane will turn off its course if there is an 
improper bend in leading or trailing edge or spars, for the amount of drift 
will be changed on one side by increased resistance. 

LATERAL INSTABILITY 

Wrong Angle of Incidence —If the angle of one wing is greater, more 
lift will be produced on that side, with corresponding decrease on the other 
wing. The airplane’s tendency will then be to fly one wing down. 

Distorted Surfaces —The same tendency to fly one wing down will be 
observed when the camber of the wing surfaces is spoiled by some distor¬ 
tion, through which the lift is made unequal. 

LONGITUDINAL INSTABILITY 

Wrong Angle of Incidence —If the lifting surface angle is too great the 
nose will rise through excess of lift and a tendency to fly tail down will re¬ 
sult. Too small an angle may cause the airplane to fly nose down. 

Occasionally, the tail plane’s angle of incidence is found to be wrong; the angle 
should be lessened if the airplane is nosing down, and increased if tail-heavy. Adjust¬ 
ments of this kind must be made with care, because longitudinal stability depends en¬ 
tirely on the tail-plane having less angle than the main lifting surfaces. 

Fuselage Warped—For the reason given above, a fuselage warped up or 
down, thereby giving an incorrect angle of incidence to the tail plane, may 
result in the airplane nosing down or being tail heavy. 

Wrong Stagger —A nose-heavy airplane will result if the top wing is 
not staggered forward to the correct degree, because the lift will then be too' 
far back. An error of *4 inch will make a material difference in longitudinal 
stability. The cause of such e 1 or is generally due to the elongation of wire 
loops or if wires have pulled the fittings into the wood. 

FLIGHT DEFECTS 

POOR CLIMB 

Excepting engine and propeller trouble, the reason for an airplane 
climbing badly is generally due to (1) too small angle of incidence; (2) 
distorted surfaces. 

LESSENED SPEED 

Excepting engine and propeller trouble, poor flight speed is generally 
due to (1) too great angle of incidence; (2) distorted surfaces; (3) skin- 
friction, from dirt or mud on surfaces. 

POOR CONTROL 

The main causes are (1) incorrect setting of control surfaces; (2) dis¬ 
tortion of control surfaces; (3) control cables badly tensioned. 

UNCONTROLLABLE ON GROUND 

When an airplane will not “taxi” straight the fault is generally due to 
(1) improper alignment of landing gear, wobbly wheels, or (2) unequal ten¬ 
sion of shock absorbers. 



Practical Aviation 


49 


REVIEW QUIZ 

Rigging the Airplane 

1. Give six important cautions about handling tools. 

2. Explain the process of assembling the landing gear. 

3. What control is first attached to the fuselage, and how? 

4. How is the vertical stabilizer fastened? 

5. Explain the assembly of rudder and elevators. 

6. What section of the wing surface is first attached to the fuselage? 

7. Should main wing sections be assembled complete before attaching? 

8. State how struts are numbered and a reason why numbering is 

essential. 

9. Give in detail the process of wing assembly with particular refer¬ 

ence to the initial adjustment of wires. 

10. Why is careful alignment of an airplane important? 

11. What are the two methods of aligning the landing gear? 

12. Describe wing alignment without stagger. 

13. What is the check for staggered wings? 

14. State how the alignment of main wing sections is verified. 

15. Explain the method which insures correct dihedral angle. 

16. Where and with what aids should the measurement be taken for the 

angle of incidence? 

17. What adjustment is made to correct for torque of the propeller? 

18. Give a rule for rigging the trailing edge ailerons. 

19. From what points are final check measurements taken? 

20. State seven general rules which govern adjustment of cables, wire 

loops and turnbuckles. 




50 


Practical Aviation 


CHAPTER ANALYSIS 

Fundamentals of Motive Power 

THE PROPELLER: 

(a) Balance. 

(b) Surface Area. 

(c) Length. 

(d) Straightness. 

(e) Care. 

THE GASOLINE ENGINE CYLINDER: 

(a) Combustion Chamber. 

(b) Piston. 

(c) Connecting Rod. 

(d) Crank Shaft. 

(e) Revolution. 

THE FOUR-CYCLE PRINCIPLE: 

(a) Intake Stroke. 

(b) Compression Stroke. 

(c) Power Stroke. 

(d) Exhaust Stroke. 

MULTIPLE CYLINDER ENGINES: 

(a) 4-cylinder Operation. 

(b) 6-cylinder Operation. 







CHAPTER VI 


Fundamentals of Motive Power 


Earlier chapters have dealt entirely with the theory of flight and the 
function and construction of the airplane as a flight medium. The student 
is now ready to consider the propulsion of the machine, upon which all theory 
of flight obtains. 

Flight is made possible, as has already been explained, by the action of 
the air on inclined surfaces driven through the air at high velocity. The 
reader is aware that the driving force is a propeller actuated by a gasoline 
engine. Consideration of the propeller will be brief, as the military aviator 
is not concerned with the details of engineering mathematics upon which pro¬ 
peller efficiency is based. Some knowledge of the method of checking up the 
balance of the air screw is all that is required of the pilot, and this is given 
on the page following. 

The study of engines must necessarily be of a general character, as the 
varying types of design in internal combustion engines make a full considera¬ 
tion of the refinements of operation a subject of voluminous proportions. The 
four chapters devoted to airplane motors give all the important points of 
information in a brief survey of the general construction and operation prin¬ 
ciples which apply to the most familiar types of aviation engines. 

The aviation engine must have small weight per horse power, minimum 
head resistance and reliability of operation; for these reasons some minor 
changes in design from familiar automobile types will be noticed. The first 
consideration is the stationary water-cooled motor; later, the rotary air¬ 
cooled types will be described. 

The student aviator is specially cautioned to apply himself to mastery 
of this chapter on engine theory. A thorough working knowledge of motors 
is required of military airmen before flight instruction is begun. A pilot who 
does not understand the principles of his motor’s operation can never expect 
to secure the best efficiency from his engine, and the ability to secure an 
extra ounce of motive power or speed is often the means of gaining a victory 
over an enemy airplane. Special emphasis is laid on the explanation of the 
four-cycle principle in this chapter; without a full understanding of these 
phases of operation the study cannot be continued intelligently. 

51 


52 


Practical Aviation 





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( $r4 ) psas 


V4T4I 


(c) Committee on Public Information 


Block test of an airplane engine with propeller attached, showing the screen protection given 
to the mechanician. The necessity for this precaution is at once obvious when 
it is known that the propeller revolves at a speed of 1,400 revolutions 

per minute 





The Propeller 


53 



Figure 43— Action of propeller revolutions 
Figures 44, 44 b — Method of propeller test for balance and area 


THE PROPELLER OR “AIR SCREW’ 

The propeller’s revolutions represent thrust, its action in screwing 
through the air (see Figure 43) translating the power of the engine into for¬ 
ward motion. The drift of the airplane, due to its resistance, is overcome by 
opposition of the thrust; it follows, therefore, that the power of the propeller 
thrust must be greater than the airplane’s drift, or the velocity will decrease. 

BALANCE 

The propeller is mounted after the airplane is assembled. It should first 
be tested for balance, for if one blade is heavier than the other it will vibrate 
when run on the engine. The usual test is shown in Figure 44. A stand is 
leveled up; a roller is then inserted in the hub of the propeller, which turns 
freely on the roller; this roller is then allowed to roll freely on the level. Any 
lack of balance is thus easily detected. 

Another method is indicated in Figure 44b. The propeller is placed in horizontal 
position and three points on the blades measured off equally distant from the center. 
By means of a spring balance weighing scale, the weights are taken at these points, 
and must correspond for each side. 

Application of more varnish on the lighter side is usually sufficient to equalize a pro¬ 
peller out of balance. 

SURFACE AREA 

Measurement of three equi-distant points by callipers should show cor¬ 
responding measurements to exactness of less than y$ inch. Figure 44b illus¬ 
trates this measurement, A being equal to A' y B to B' and C to C’ . 

LENGTH 

Blades should be of equal length to 1-16 inch. 

STRAIGHTNESS 

With the propeller mounted on a shaft an object should be fixed in a 
position where the tip of one blade grazes it. With the point marked, the 
other blade is brought around and should come within */§ inch or graze it. 

CARE OF PROPELLERS 

They should never be leaned against a wall or allowed to remain long in horizontal 
position. 

They should not be stored either in very damp, or very dry, places. 

They should not be stored where the sun will shine on them. 

The proper method of storage is hanging in vertical position on horizontal pegs. 



























54 


Practical Aviation 



(c) Committee on Public Information 

This picture, take' at one of the “Ground Schools" of the Army Signal Corps, well illustrates 
the earnestness and concentration of the men. The instructor is obviously hairing no dif¬ 
ficulty in keeping his men at work, for these future American airmen know just as well 
as he how vital it is that they should understand every impulse of the engine which 
will soon mean so much to them in midair. A most thorough and fundamental 
course of training in engines is necessary for the men who carry the respon¬ 
sibility for America’s warfare in the skies 








The Gasoline Engine Cylinder 


55 



THE GASOLINE ENGINE CYLINDER 

Vaporized gasoline mixed with air and set afire by an electric spark re¬ 
sults in combustion (explosion), the intense heat from which develops the 
pressure which operates the engine. 

Figure 45 shows a single cylinder of a gasoline engine in sectional view. The 
names of the parts should be studied. 

COMBUSTION CHAMBER 

The closed end of the cylinder, in which the combustion takes place, is known as the 
cylinder head, the space between it and the piston being the combustion chamber. 

PISTON 

This is a cylindrical-shaped body which slides back and forth in the cylinder, the 
combustion (explosion) driving it downward. 

CONNECTING ROD 

Suspended from the piston is a connecting rod which acquires a reciprocating motion 
as the piston moves up and down. 

CRANK SHAFT 

The connecting rod is attached to the crank shaft, by means of which the reciproca¬ 
ting motion is changed to a rotary motion (as a wheel revolving on its axis) which turns 
the propeller. 

REVOLUTION 

A complete turn of the crank shaft, moving the piston down and back, is called a 
revolution. 









































































56 


Practical Aviation 


THE FOUR-CYCLE PRINCIPLE 

There are two types of internal combustion engines using gasoline for 
motive power; viz.; the two-cycle and the four-cycle. These may be distin¬ 
guished by considering them as two-stroke and four-stroke engines. The two- 
cycle engine has no valves, the gas entering and exhausting through ports 
in the cylinder walls, covered and uncovered at proper intervals by the travel 
of the piston up and down. The four-cycle engine, which will be considered 
exclusively in the text following, as its use is almost universal in aviation, has 
intake and exhaust valves operated by mechanical means. 

Figures 46, 47, 48 and 49 show the action of the four-cycle engine, clearly 
indicating the operations during the four ^strokes. 

INTAKE STROKE T 

✓ 

Suction caused by the piston starting downward, as the engine is “cranked,” draws 
the explosive gasoline vapor into the combustion chamber of the cylinder. It enters 
through the intake valve, which is the only opening. The exhaust valve is closed, the 
intake valve being so adjusted that the cam opens it mechanically as the suction action 
of the piston commences. 


COMPRESSION STROKE 

Both valves are closed as the piston starts on its up-stroke and the explosive mixture 
in the cylinder is compressed into the small space of the combustion chamber as it 
reaches the top of the stroke. 

The explosive value of compression may be illustrated by considering the action 
of gunpowder, which, ignited in the open air burns slowly but is instantly exploded if 
confined to a small chamber. 


POWER STROKE 

As the piston reaches the top the spark is timed to jump the spark gap points and 
ignite the explosive vapor. The piston is driven ddwn by the expansion of the gas, 
making the power stroke. 


EXHAUST STROKE 

As the piston returns from the power stroke the exhaust valve is opened, the pres¬ 
sure from the explosion forcing out the burned gas. The upward move of the piston 
pushes out all of the burned gas that does not escape by its own pressure. 

# 

The exhaust valve closes as the piston reaches the top, and the inlet valve opens to 
admit a fresh charge of gas into the cylinder. The operation is then repeated as long as 
the engine runs. 



The Four-Cycle Principle 


57 


Figure 46 







Figure 47 




F/gure 46 Figure 49 

Figure 46 —Intake stroke Figure 47 —Compression stroke Figure 48 —Power stroke 

Figure 49 —Exhaust stroke 

THE FOUR-CYCLE PRINCIPLE 

FIGURE 46 , . 

This is the intake stroke. The inlet valve is open and the gas is entering the cylin¬ 
der, drawn by the suction of the piston. 

FIGURE 47 , 

This is the compression stroke. Both valves are closed and the piston is returning, 

the upward stroke compressing the gas. 

FIGURE 48 . , , , , , . . 

This is the power stroke. The electrical spark from the spark plug ignites the gas. 

Both valves are closed as the combustion drives the cylinder downward. 

FIGURE 49 

This is the exhaust stroke. Only the exhaust valve is open, the upward movement 
of the piston forcing the burned gases out of the cylinder. 













































58 


Practical Aviation 



Figure 50 —Cross section of a 4-cylindcr engine 


MULTIPLE CYLINDER ENGINES 

A cycle operation requires four strokes to two revolutions. Only one of the four 
strokes is a power stroke; therefore, in a single cylinder engine the piston must be car¬ 
ried through three dead strokes. This ordinarily requires a heavy fly wheel, which when 
started will continue to revolve. It is obvious that the more cylinders an engine has the 
steadier will be the power impulses, since the successive explosions may be timed to 
follow so closely that one of the pistons will always be on a power stroke. Thus in avia¬ 
tion engines where weight is a material factor, the heavy fly-wheel is dispensed with by 
use of multiple cylinder engines. 

4-CYLINDER OPERATION 

Four-cylinder engines deliver a power impulse every stroke, or two power impulses 
to every revolution. 

Figure 50 thr-vs a 4-cylinder engine in cross section. 

It will be n ed that the crank shaft which delivers motion to the propeller is set 
at 180 degrees, the end pair being a half-revolution from the inside pair. 

As piston No. 1 descends on the power stroke, No. 2 is coming up on exhaust; No. 
3 is ascending on compression and will be fired next; No. 4 is taking y\ gas. 

FIRING ORDER 

The rotation in which the explosions take place in the cylinders is therefore 1, 3, 4, 2. 

This engine could as well fire 1. 2, 4, 3, but it will be obvious that explosions in the 
order 1, 2, 3, 4 would require a crank shaft alternately projecting to each side, 1 and 3 
being up when 2 and 4 are down. This construction has the following disadvantages: 

(a) A crank shaft weaker and more difficult to make. 

(b) A rocking motion, or vibration, from side to side. 

The alternate distribution of power impulses, when cylinders are fired in the order 
shown in the illustration, makes for smooth running. 





























































































































































Multiple Cylinder Engines 


59 



Figure 51— Cross section of a 6-cylinder engine 





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6 Cylinder Motor 


Figure 52— Graphic illustration of cylinder 
operation in 4- and 6-cylindcr 
engines 

6-CYLINDER OPERATION 

The 6-cylinder engine is four-cycle, the same as the 4-cylinder engine. The principal 
differences in construction are in the addition of more cylinders and consequent change 
in crank shaft. 

Figure 51 shows a cross section of the 6-cylinder engine. 

It will be noted that the crank shaft is arranged to turn two revolutions during four 
strokes, as in the case of the 4-cylinder engine. The crank shaft is therefore divided 
into three pairs of throws, i.e., each pair is placed at 120 degrees, or 1-3 of a circle 
apart. The pairs are: 1 and 6, 2 and 5, 4 and 3. 

FIRING ORDER 

In Figure 51, cylinder No. 5 has just fired, No. 3 will fire next, after which the 
order will be 6, 2, 4, 1. 

With 4-cylinder engines an explosion takes place each half-revolution; the 6-cylin¬ 
der engine in the same half-revolution has 1*4 explosions. That is, power impulses are 
continuous in 6-cylinder engines, in fact they overlap; this results in smooth running. 

Figure 52 is a graphic representation of the sequence of cylinder operation in 
4-cylinder and 6-cylinder types of engines, showing how power impulses overlap in the 

latter. 
























































































































































































































































60 


Practical Aviation 



(c) Committee on Public Information 


The construction of the lower half of the crank case and the method of supporting the 
crank shaft arc clearly shown in this photograph. An interesting feature of the illustration 
is the cradle in which the crank case rests; it is so constructed that the successive assembly 
of engine parts may be made and the engine turned around so as to be at any angle with 
the door. Since the introduction of this cradle the mechanician is no longer required to 

lie on his back and work upwards 






Practical Aviation 


61 


REVIEW QUIZ 

Fundamentals of Motive Power 

1. What is the aerodynamic force which the power of the propeller 

thrust must overcome? 

2. How is a propeller tested for balance? Give two methods. 

3. When a propeller is out of balance how is the lighter side usually 

equalized? 

4. State how surface area measurement of the propeller is taken. 

5. What is the test for straightness? 

6. Give four rules for care of propellers. 

7. Explain how the motive force is produced in the cylinder of an 

engine. 

8. Name and define three moving parts which transmit the motion. 

9. State the difference between a two-cycle engine and a four-cycle 

engine. 

10. Describe in detail the four phases or operations of the four-cycle 

engine. 

11. What operating advantage is gained by increasing the number of 

cylinders? 

12. How many power impulses per revolution are delivered by a 4- 

cylinder engine? 

13. In a 4-cylinder engine, at what degree angle are crank throws set? 

14. Explain why the four cylinders are not fired in successive order. 

15. In what important particular does the 6-cylinder engine differ from 

the 4-cylinder? 

16. How are the throws of the crank shaft arranged for six cylinders? 

17. Give a proper firing order for a 6-cylinder engine. 

18. In a half-revolution, how many explosions take place in the six 

cylinders? 

19. State an advantage gained when power impulses overlap. 

20. Compare the sequence of operation in 4-cylinder and 6-cylinder 

engines, 



62 


Practical Aviation 


**V*yws 


CHAPTER ANALYSIS 

Pistons, Valves and Carburetors 


THE PISTON: 


(a) 

Construction. 

(b) 

Piston Rings. 

(c) 

Connecting Rod. 

(d) 

Wrist Pin. 

CRANK 

SHAFT: 

(a) 

Construction. 

(b) 

Attachments. 

CRANK 

CASE: 

(a) 

Construction. 

(b) 

Mountings. 

VALVES AND VALVE MECHANISM 

(a) 

Camshaft. 

(b) 

Cams. 

(c) 

Exhaust Valve. 

(d) 

Inlet Valve. 

(e) 

Valve Operating Mechanism. 

(f) 

Valve Clearance. 

CARBURETION: 

(a) 

Principle of the Carburetor. 

(b) 

Construction. 

(c) 

Duplex. 

(d) 

Manifolds. 







CHAPTER VII 


Pistons, Valves and Carburetors 


Continuing the subject of aviation engines, a few considerations may be 
noted, preliminary to the study of pistons, valves and carburetors. 

Firs"' is the refinement of design necessary for aeronautical work. The 
aviation engine, unlike those of motor cars, ordinarily uses 7 5 per cent, of 
its horsepower, as against one-quarter usage in motor cars. 

A second consideration of design is the necessity for building an aviation 
engine as light as possible, yet the punishment of material within the engine 
structure is about fourteen times as severe as in the motor car. The effect 
is demonstrated in the respective lives of both types. A motor car engine 
generally runs up to a mileage of 25,000, at a maximum average speed of 25 
miles per hour, or completes 1,000 hours operation before overhauling is 
necessary. The aviation engine, with a speed of 100 miles an hour, requires 
a complete overhaul in about 50 flying hours, a total of 5,000 miles, or one- 
fifth of the motor car's mileage. 

These comparisons broadly illustrate the relative severity of the two 
types of engine service. But although it is required that the aviation engine 
be of light construction, strength must not be sacrificed in vital parts. While 
light weight is the aim in designing the crank shaft and crank case, main 
bearings, crank and piston bearings, strength is maintained by very careful 
selection of materials. 

An airplane required to make climbs of 20,000 feet must necessarily have 
perfect reliability of operation. The structure of the aircraft is obviously sen¬ 
sitive to vibration and an engine which does not function smoothly materi¬ 
ally impairs flight efficiency. Irregular impulses of the engine also affect its 
light structure and uniform explosions are a requisite. This uniformity is 
gained only through perfect distribution of gas to the cylinders. 

The student should keep these conditions in mind as the study of vital 
parts of the engine is continued. 


63 


64 


Practical Aviation 




3 - cross secf/on of piston 



C* concentric 
piston ring 



Figure 53 —Details of the piston and connecting rod 

PISTON 

Although one of the simplest parts of the airplane motor, the piston is 
one of the most important, as it receives the full force of the explosion and 
transmits the gas combustion into power. 

In construction, it shows only slight variations in the numerous types of engines; the 
most common form of construction is shown at A and B in Figure 53. The piston is made 
usually of cast iron, steel or aluminum, machined to fit the cylinder diameter with a clearance 
of .005 to .010 of an inch to compensate for the expansion of heat and permit lubrication 
between it and the cylinder walls. The clearance varies with the designed speed of the motor, 
increasing for the higher speed motors in which greater friction is created. Channels are 
cut in the outer face of the piston wall, near the top; in these the piston rings are placed. 

PISTON RINGS 

These are split rings of cast iron, sprung so as to bear tightly against the 
wall of the cylinder to prevent leakage of gas from the combustion chamber 
and the passage of lubricating oil into the explosion area. Two types are 
shown at C and D in Figure 53, and the common forms of expansion joints 
at E and F. 

CONNECTING ROD 

The connecting rod joins the piston to the crank shaft and transmits the 
motion to the latter as the piston travels up and down. It is usually made 
of drop forged steel, I-beam construction. 

A typical connecting rod is shown at H in Figure 53, which indicates the two bearings, 
the upper, of bronze, connected to the wrist pin, and the lower bearing, through which the 
crank shaft passes, usually split and made of a bronze base with babbitt metal carefully 
scraped to exact clearance. 

WRIST PIN 

This fitting, also known as the gudgeon or piston pin, joins the piston to 
the connecting rod. As shown at G in Figure 53, it is a simple cylindrical 
element, usually made of steel and fitting the bosses closely. 











































































































Crank Shaft and Crank Case 


65 



Ceors dr/r/ng 
oil pump 



Figure 54 ( upper)—Crank shaft of 6-cylinder engine 
Figure 55 {lower)—Lower section of crank case with shaft in position 


CRANK SHAFT 

As the main drive shaft of the motor, the crank shaft is subjected to 
greatest strain; it is therefore ordinarily made of high tensile steel, drop or 
machine forging. It is constructed as a bar having U-shaped offset arms, or 
crank-throws, one for each cylinder, for attachment to the connecting rods. 
It is usually drilled for oil ducts and hollowed to reduce weight, yet is of 
requisite strength to withstand the continuous shocks it sustains. 


A crank shaft for a 6-cylinder engine is shown in Figure 54, with four of the con¬ 
necting rods attached and the propeller hub and flange shown at the right end. The 
opposite end carries a gear which meshes with a system of gears to transmit motion to 
the camshaft, magneto, oil pump and other auxiliary parts. 

In the illustration provision is made for mounting the propeller on the crank shaft 
for direct drive, in which case a flywheel would not ordinarily be used. Because the 
speed of the motor is generally considerably higher than the most efficient number of 
revolutions per minute of the propeller, reduction gears are commonly introduced at the 
propeller end of the crank shaft where the motor speed exceeds 1,400 revolutions per 
minute. 

CRANK CASE 

The crank case is usually made of aluminum alloy, in two parts, the 
upper, to which the cylinders are bolted, and the lower containing the crank¬ 
shaft and lubricating oil. It contains the crank shaft bearings, or seats, in 
which the center line of the crank shaft is supported. These mountings are 
usually made of babbitt or other high anti-friction metal. 

Figure 55 shows the lower half of a typical crank case for a 6-cylinder engine, the 
shape of the case conforming to the type of the motor in each instance. 


































66 


Practical Aviation 



Figure 5 7b {right)—Valve operating mechanism where camshaft is at base of motor 

VALVES AND VALVE MECHANISM 

CAMSHAFT 

The shafts for operating the cams, irregularly curved lugs which operate 
the valve mechanisms, are known as camshafts. The material generally used 
is open hearth or drop-forged steel; the bearings are of bronze. Camshafts 
are drilled to reduce weight. 

Two methods of driving or rotating the camshaft are employed, the most 
common being by means of gearing, a simple spur gear such as shown at the 
left of Figure 56 being employed when the camshaft is horizontal, or parallel 
to the crank shaft, from which it obtains its motion at half-speed. 

Operation through use of a chain drive in the form of link belts over toothed pul¬ 
leys, is the second method, recently come into some favor through its use in foreign 
engines. 

CAMS 

A cam is a lug cast integrally on the camshaft and machined to a form 
resembling a circle, with an approximately triangular projection at one point. 
It is this projection which acts on the valve mechanism as the shaft rotates. 

Figures 57a and 57b show cams operating on overhead valves, the former acting direct 
on rocker arms and the latter through the medium of a tappet rod. Both inlet and exhaust 
valves are operated by the same camshaft in general practice, although many exceptions are 
made in engines which have separate camshafts for intake and exhaust valves. 

VALVES 

In almost every instance, aviation motors have valves placed in the head 
of the cylinder, or overhead valves, thereby gaining increased power. The 
valves are opened by the mechanism operated by the camshaft and closed by 
springs. 


































Valves and Valve Operation 


67 


EXHAUST VALVE 

Exhaust valves are generally made of tungsten steel, which has the 
necessary high resistance to the heat of the exploded gases which pass through 
the exhaust. The disk and valve seat are beveled and ground so that the 
valve is gas-tight when seated. 

Theoretically, the exhaust valve is opened only during one of the four 
cycles or phases of the engine’s operation, that is on the upward exhaust 
stroke. In practice, however, it is usually opened as soon as the piston has 
moved downward through about seven-eighths of its power stroke, or y 2 -inch 
from bottom dead center. It closes exactly at the finish of the exhaust stroke, 
or in some cases it is allowed to remain open until the piston has moved 
down about 1-20-inch on its intake stroke, so that all exhaust gas has a 
chance to escape. 

The exhaust ports are of proper dimensions, varying with type of engine, to insure 
rapid and complete expulsion of the burnt gas. Exhaust manifolds are seldom used as 
they retard this expulsion, but short pipes are common, permitting the gas to exhaust 
into the open air but carrying it away from the aviator’s face, and reducing the danger 
from fire. 

INLET VALVE 

High nickel steel or cast iron are the materials generally used for inlet 
valves. The construction of valve and seat is identical with the exhaust 
valves, usually beveled and always ground so as to be leak-proof when closed. 

The inlet valve is timed to open when the piston has descended about 
3^-inch on its intake stroke, and remains open until the piston has traveled 
about ys~in ch up on the compression stroke. This permits the cylinder to 
fill with gas, the downward drive of the piston creating a suction which will 
remain stronger than the slight upward pressure created during the 200th 
part of a second in which the valve remains open as the upward compression 
stroke begins. 

VALVE OPERATING MECHANISM 

Valve-in-the-head motors gain flexibility by offering no resistance to 
the entrance of gas into the combustion chamber, or impediment to straight 
exhaustion. But the valve opening mechanism is somewhat more compli¬ 
cated than that used in T-head or L-head cylinders. In place of the direct 
push rod action from the cams employed by the latter, the valve in the head 
motor secures its opening of valves by the system of rods and rocker arms 
illustrated in two forms, respectively in Figures 57a and 57b. 

In Figure 57b, the camshaft is located at the base of the cylinders, or at 
the crank case, being rotated by bevel gears at half speed from the crank 
shaft. The cam pushes up the tappet rod, raising the rocker arm at one end, 
which pushes down the valve attached to the other. 

Figure 57a shows a form of construction which places the camshaft 
above the cylinders, where it is driven by bevel pinion and gear drive by a 
vertical countershaft from the crank shaft. This form of construction is 
being adopted by many American aviation engine manufacturers, since it 
does away with the tappet rods and simplifies the engine construction. 

All valves are closed by the action of the spring, as clearly indicated in 
the drawings. 

VALVE CLEARANCE 

Space must be left between the valve stem and the actuating means, the amount 
of clearance depending upon the design of the engine. The clearance is indicated as 
.020 inch in Figure 57a, where the valve stems are long; in the Curtiss 0X2 engine the 
clearance is .010 inch, or half, the variation being due to the amount of valve area which 
becomes heated and expands in length when the engine is running. 




68 


Practical Aviation 


Priming tube D 


fkxit 


Goso/ine 

mtet 



To thro We 

j 


- . Butterfly f 

'.^Secondary well E 

Choke 
Nozzle 6 
Cap Jet C 

Mom 
Jets 


Compensator A 



Buet/ntet 


* 


Figure 58 {left)—Sectional view of carburetor showing details of the compound nozzle and 

compensator 


Figure 59 (right)—The duplex carburetor for multiple cylinder engines 


CARBURETION 

Gasoline will not burn unless it is mixed with air. To burn with great 
rapidity and heat, or to “explode,” as required by the internal combustion 
engines of aviation, the air must be in correct proportion to the gasoline 
vapor; these proportions range from 18 to 20 parts of air to one of gasoline. 
The vapor is produced by exposing the liquid to the air, generally by spray¬ 
ing into a mixing chamber. 

PRINCIPLE OF THE CARBURETOR 

The device in which the vaporizing of gasoline is performed is termed 
a carburetor. There are numerous types used on airplanes, but the standard 
construction calls for: (a) a float chamber to maintain the gasoline at a con¬ 
stant level, (b) a mixing chamber where the gasoline is sprayed through a 
nozzle and mixed with incoming air. In the form of vapor it is then drawn 
through the inlet valve into the cylinder by the suction of the down stroke 
of the piston. 

The throttle valve, or butterfly, generally placed above the spray nozzle 
in the mixing chamber, regulates the amount of gas entering the cylinder; 
this valve is controlled by a lever near the pilot’s seat. The speed of the 
engine increases with the opening of this throttle and decreases accordingly 
as it is closed. 

A float with a needle valve cuts off the flow of gasoline when the engine 
is not running. 














































































Carburetion 


69 


CONSTRUCTION OF THE CARBURETOR 

Figure 58 is a sectional view of the Zenith carburetor, selected as typical 
of the best construction and widely used in American aviation engines. By 
a compensator and compound nozzle principle, this carburetor maintains a 
constant ratio of air and gasoline at the most efficient combustion mixture. 

The advance in design here represented is the elimination of variable air 
valves or moving parts. The construction is clearly indicated in Figure 58. 
Gasoline from the float chamber is admitted at compensator^ into the priming 
tube D, extending into the secondary well E, and opening at the priming hole 
uncovered by the action of the butterfly valve F. The suction at the priming hole 
is powerful and with the butterfly partly open the well full of gasoline is drawn 
into the cylinders, effectively priming the motor. 

At high speeds with the butterfly opened further, the priming well 
ceases to operate and the compound nozzle drains the well. It is this feature 
of the Zenith carburetor which counteracts the defects of the vaporization 
at the nozzle of the conventional carburetor when the engine is operating 
at low speed. 

To illustrate: In the conventional single jet carburetor the gasoline 
enters by suction through main jet B, spraying from nozzle G in the path of air 
entering through the inlet at the lower right of the drawing, Figure 58. As the 
speed of the motor increases, the air flow increases, but the law of flow of liquid 
bodies makes the flow of gasoline from the jet increase faster, giving a mixture 
which increases the percentage of gasoline, or becomes richer. By the introduc¬ 
tion of the secondary well E, the gasoline is fed through the compensator A and 
is not affected by the suction, since the well is open to atmospheric pressure. 
The flow of gasoline is therefore made constant at all speeds, it being obvious 
that as the air intake increases with greater speed, the mixture becomes 
poorer. The combination of the two results in a carburetor giving a constant 
mixture. 

DUPLEX CARBURETOR 

For multiple cylinder aviation engines, arranged in V form, which will 
be discussed later, it was found that the strong cross suction in the inlet 
manifold made good carburetion difficult with a single carburetor. The 
development of the duplex carburetor, shown in Figure 59, followed. It 
provides two separate mixing chambers, fed by a common float chamber 
and permitting each set of cylinders a separate intake. 

MANIFOLDS 

As the gas mixture passes upward and out of the mixing chamber it 
reaches the cylinders by way of pipes divided into branches built to accom¬ 
modate the model of motor, and termed manifolds. The branches of the 
manifold are of the same dimensions, so as to obtain the same results for 
all cylinders and are free from sharp bends or obstructions which might 
retard the progress of the gas to the cylinders. 






70 


Practical Aviation 























Practical Aviation 


71 


REVIEW QUIZ 

Pistons, Valves and Carburetors 


1. Compare the average life of a motor car engine and an aviation 

engine. 

2. Describe the construction of the piston. 

3. What is the purpose of the piston rings? 

4. Name two types of piston rings. 

5. How is the connecting rod constructed? 

6. Give two additional names for the wrist pin. 

7. State the material of which the crank shaft is constructed and 

describe its features. 


8. Are propellers always mounted on the crank shaft for direct drive? 

9. Explain the construction of a crank case. 

10. Give two methods of rotating the camshaft. 

11. Describe a cam and how it operates a valve. 

12. In what portion of the engine are valves usually placed and how 

are they closed? 

13. Why is the exhaust valve generally made of tungsten steel and 

how is it made gas-tight? 

14. Give the essential differences in valve operating mechanisms which 

employ tappet rods and those having rocker arms. 

15. Why is valve clearance necessary? 

16. State what change is necessary in gasoline before it will explode. 

17. What is the principle of the carburetor? 

18. Describe in detail the construction and operation of a compound 

nozzle carburetor. 

19. How many float chambers has the duplex carburetor used for 

V-motors? 

20. Name the engine part through which the gas passes to the com¬ 

bustion chamber. 




72 


Practical Aviation 


CHAPTER ANALYSIS 


Ignition, Cooling and Lubrication 



IGNITION: 

(a) Magneto. 

(b) Distributor. 

(c) Condenser. 

(d) Circuit Breaker. 

(e) Spark Plug. 

COOLING: 

(a) Water Cooling. 

(b) Air Cooling. 

LUBRICATION: 

(a) Splash. 

(b) Force-feed. 




CHAPTER VIII 


Ignition, Cooling and Lubrication of Engines 

Supplemental to the description and definition of function of valves 
contained in the previous chapter, the student will find a knowledge of valve 
setting and valve timing of value. Instruction in these two operations, as 
officially given for the Curtiss engine, follow: 

Valve Setting—After grinding and cleaning, set the inlet valves at 0.010 
clearance and the exhaust valves at 0.010 clearance. This setting should be 
done on each cylinder just after inlet valve has closed. If the stem is 
indented due to any cause, remove the valve and grind the stem end to a 
flat surface. 

Valve Timing—After setting the clearance, turn the engine in the direc¬ 
tion of rotation till the piston of No. 1 cylinder is 1/16 inch past top center. 
Then turn the camshaft in its direction of rotation till the exhaust valve of 
No. 1 cylinder has just closed. Put on the camshaft gear, being sure that 
the keyway of the gear lines up with the key in the camshaft. 

Thus set and timed, the inlet valves will open 12 degrees past top center 
and close 40 degrees past bottom center; the exhaust valves will open 45 
degrees before bottom center and close on top center. 

As it is now purposed to consider ignition and its relation to the efficient 
operation of the aviation engine, these further practical suggestions on timing 
may well be included. 

Magneto Timing—Turn the engine in the direction of rotation till the 
intake valve of No. 1 cylinder has closed; then turn the engine in the same 
direction till the piston of No. 1 cylinder is on top dead center; then turn the 
motor backward till the piston of No. 1 cylinder is 54 inch from top center. 
Turn the armature of the magneto in the direction of its rotation (it is the 
same as that of the crank shaft) till the distributor brush is on No. 1 segment 
with the breaker points just ready to open. Put on the magneto gear, using 
the same precaution as given for engaging the camshaft gear. This should 
bring the firing-time of all cylinders to 30 degrees before top center. 

The spark advance lever should be in position of full advance during 
this whole operation. The gap between the breaker points should be 0.018 
inch and that of the spark-plug points 0.023 inch. 

73 


74 


Practical Aviation 



Figure 61 —A high Figure 62a—Construction of spark plug Figure 63 —Construction 

tension magneto Figure 62b—General view of spark plug of the magneto 

IGNITION 

To set afire the compressed gas mixture in the cylinder at the proper 
time an electric spark is produced in the combustion chamber, through the 
medium of a spark plug, the points of which offer a break in the ignition 
circuit, causing the current to jump the gap and spark. The essentials of an 
ignition system for aviation engines are, (a) a method of producing the cur¬ 
rent, (b) timing apparatus to regulate the sparking at the proper instant in 
each cylinder, (c) wiring and auxiliary devices to carry the generated current 
to the spark plug in the cylinder. 

MAGNETO 

Aviation motors are equipped with high-tension magnetos, i.e., those with a second¬ 
ary winding of fine copper wire over the primary winding, as distinguished from the 
low-tension type with primary coil only. In the coarse wire winding, or primary (on 
top of which is the secondary winding of fine wire) a low-tension current is generated 
as the armature revolves between the ends of the magnets. This low-tension current 
then flows to the circuit breaker, where it is broken by the points operated by a cam. 
The current then goes to a condenser for storage until the points again close. Break¬ 
ing the current creates a high-tension current which flows to the distributor and spark 
plugs. 

Figure 61 shows the Berling high-tension magneto, used on Curtiss engines and 
one of the best of the representative types; Figure 63 shows the construction. 

DISTRIBUTOR 

The distributor is the device wherein both the primary and secondary currents gen¬ 
erated by the magneto are collected by a brush and distributed to the proper cylinder 
at the proper time. 

CONDENSER 

Absorption of the self-induced current of the primary winding, thereby preventing 
it opposing the rapid fall of the primary current, is the function of the condenser. 

CIRCUIT BREAKER 

This device keeps the circuit closed except at the time of sparking. 

SPARK PLUG 

This device consists of an insulating member screwed into the cylinder and carrying 
the terminal electrodes across which the spark for ignition jumps. The secondary wire from 
the coil is attached to a terminal at the top of the central electrode. Details of construction 
of the spark plug are shown in Figures 62a and 62b. 

Spark plugs are screwed into the combustion chamber directly in the path of the incoming gases from 
the carburetor. On most aviation engines a double set of plugs is used, two to a cylinder, igniting the 
mixture at two different points and thereby gaining twenty-five per cent motor power at high speed. 
















































Water and Air Cooling 


75 



Figure 64—Radiator at front Figure 65a— Water-cooled Figure 65 b — Air-cooled 

of fuselage cylinder cylinder 


COOLING 

The intense heat of the explosions in engine cylinders would heat the 
metal portions to a point where the lubricating oil would be burned and 
become useless and the piston rings expand and bind in the cylinder walls, 
if a means of cooling was not provided. There are two general systems of 
cooling: (a) water cooling; (b) air cooling. 

WATER COOLING 

This system consists of a circulation of water through jackets which 
surround the heated portion of the cylinder wall; a radiator, constructed of 
thin metal tubes with a large exposed surface area, wherein the water is 
cooled; and a means of keeping the water in circulation from the cylinder 
jackets to the radiator, and back again through the system. 

Figure 64 illustrates one form of radiator, constructed at the front of 
the fuselage with provision for the propeller hub. 

Figure 65a is a view, partly in section, of a cylinder with water jacket cast 
integral. 

The water is circulated either by a pump which is gear-driven from the 
motor, or it is automatically circulated by the thermo-syphon principle, which 
utilizes the tendency of heated water to rise. 

When the airplane is at its angle of steepest climb maximum heating of the motor 
occurs. For this reason, radiators are constructed so the cells are not horizontal, but 
parallel to a tangent of the mean trajectory of climb. 

AIR COOLING 

Cooling flanges, or metal fins, are radiated from the cylinder walls in 
the air-cooled type of engine, to absorb the heat of the explosions and diffuse 
it in the rush of air. The cylinders are placed directly in the path of the 
propeller slip stream and often a powerful fan is used to increase the rate 
and degree of cooling. 

Figure 65b shows an air-cooled cylinder, partly in section. 

The principal advantage of air cooling is reduction of weight through the elimina¬ 
tion of the various parts of the water cooling system. Rotary radial cylinder types have 
proved practical with air cooling, but it is generally conceded that the water-cooled 
motor is best for long flights. 

































































76 


Practical Aviation 


Oil overflow 


OH rings on piston 
circu/ote oil into hollow 
wrist pin. 

Oil overflow lubricates \ 
gears, excess oil flowing [ 
down through magneto , 
gear housing into sump 

i 

Individual oil pipe to 1 : 
each cylinder aufomd 
tically injecting on ¬ 
to pistons as each 
one passes oil port 

Relief valve through which J 
excess oil flows back into sump 



Cam shaft oiling through 
auxiliary hancfpump 

Oil flowing, from cooling resevoirs 
into mam oil pipe. 


Leads to boffom of each 
main bearing. 


- Itol/ow crank pin for 
oiling conn rod bearing 

Baffle P/ates 
Sump andresevo/r of oil 

0i/\ strainer 


Figure 66 —A modern oiling system for aviation engines 


LUBRICATION 

The necessity for providing some means of preventing excessive friction 
between swiftly moving parts is due to the heating which would result if a 
lubricant was not applied between them. The temperature of the aviation 
engine as a whole is an additional reason for insuring proper oiling of parts. 

Two types of motor lubrication are in use: 

(a) Splash lubrication—Oil is held in the sump, or reservoir at the 
bottom of the crank case, and splashed on the moving parts by the revolu¬ 
tions of the crank shaft. 

(b) Force-feed—Positive mechanical means deliver the oil under pres¬ 
sure to the various working parts of the engine. 

Owing to the evolutions of the airplane in flight, lubricating systems have been 
elaborated to deliver oil as needed to all working parts and to eliminate the possibility 
of flooding cylinders. 

FORCE-FEED LUBRICATION 

Figure 66 gives a clear illustration of a modern oiling system for aviation engines; 
in this instance, the Hall-Scott engine, representative of the best practice in lubrication. 

The crank shaft, connecting rods and all other parts within the crank case and 
cylinders are lubricated directly or indirectly by a forced-feed oiling system. The cylin¬ 
der walls and wrist-pins are lubricated by oil spray thrown from the lower end of the 
connecting rod bearings. The oil is drawn from the strainer located at the lowest por¬ 
tion of the crank case, forced around the main intake manifold jacket. From here it is 
circulated to the main distributing pipe located along the lower left hand side of the 
upper portion of the crank case. Tht* oil is then forced directly to the lower side of the 
crank shaft, through holes drilled in each main bearing cup. Leakage from these main 
bearings is caught in scuppers placed upon the cheeks of the crank shaft, furnishing oil 
under pressure to the connecting rod bearings. 

A bi-pass located at the front end of the distributing oil pipe can be regulated to 
lessen or raise the pressure. By screwing the valve in, the pressure will raise and more 
oil will be forced to the bearings. By unscrewing, pressure is reduced and less oil is fed. 

Independent of the above-mentioned system, a small, directly driven rotary oiler 
feeds oil to the base of each individual cylinder. The supply of oil is furnished by the 
main oil pump located in the lower half of the crank case. A small sight-feed regula¬ 
tor controls the supply of oil from this oiler. This instrument is placed higher than the 
auxiliary oil distributor itself to enable the oil to drain by gravity feed to the oiler. 

The oil sump plug is located at the lowest point of the crank case. This is a trap 
for dirt, water and sediment and is removed by unscrewing. Oil is furnished mechanic¬ 
ally to the camshaft housing under pressure through a small tube leading from the 
main distributing pipe at the propeller end of the engine directly into the end of the 
camshaft housing. The opposite end of this housing is amply relieved to allow the 
oil to rapidly flow down upon camshaft, magneto, pinion-shaft, and crank shaft gears, 
after which it returns to the lower crank case. An outside overflow pipe is also pro¬ 
vided to carry away the surplus oil. 









































































































Practical Aviation 


77 


REVIEW QUIZ 

Ignition, Cooling and Lubrication of Engines 

1. What valve in the first cylinder should be closed as the initial step 

in magneto timing? 

2. Explain the next steps up to the time when the magneto gear is 

put on. 

3. What should be the position of the spark lever during the timing 

operation? 

4. Give the dimensions of the gap between breaker points. Spark plug 

points. 

5. Why is ignition required in aviation motors? 

• \ 

6. What comprises an ignition system? 

7. State the principal construction difference between a high-tension 

magneto and a low-tension magneto. 

8. Briefly explain how the high-tension magneto generates low-tension 

current and changes it to high-tension current. 

9. What purpose is served by the distributor? 

10. Define the functions of the condenser and the circuit breaker. 

11. Describe the spark plug and give the reason why aviation engines 

usually employ a double set. 

12. Why is provision for cooling an engine required? 

13. Name the principal parts of a water cooling system and explain 

how circulation is gained. 

14. What differences in construction of cylinder walls are made for 

air cooling? 

15. State the principal advantage gained by air cooling. 

16. In what way is water cooling superior? 

17. Give two reasons why lubrication of engines is necessary. 

18. Name the two types of motor lubrication and explain how they 

differ. 

19. How are parts within crank case and cylinders oiled by a force- 

feed system? 

20. How are dirt, water and sediment removed? 




78 


Practical Aviation 


CHAPTER ANALYSIS 

Types of Motors, Operation and Care of Engines 

BORE AND STROKE RATIO: 

(a) Long - Stroke. 

(b) Short Stroke. 

V-TYPE MOTORS: 

(a) 8-Cylinder. 

(b) 12-Cylinder. 

(c) The Liberty Motor. 

ROTARY ENGINES: 

(a) Elements of Design. 

(b) The Gnome Engine. 

STARTING THE ENGINE: 

(a) Preparatory. 

(b) Swinging the Propeller. 

(c) Signals. 

(d) Self-Starters. 

FUEL CONSERVATION IN FLIGHT: 

(a) Speed. 

(b) Altitude. 

CARE OF ENGINES: 

(a) General Rules. 

(b) The Trouble Chart. 






CHAPTER IX 


Types of Motors, Operation and Care of Engines 


Fundamentals of the theory of operation and construction of aviation 
engine parts have been covered in sufficient detail for the student aviator 
in previous chapters. It but remains to consider as types, a few of the more 
advanced engines, and the balance of motor instruction may be safely left to 
shop practice, where actual assembly should be undertaken. The engineering 
factors which enter into the design of motors can be made a supplementary 
study, if desired, but the air pilot of wartime is not required to have the 
full mathematical knowledge of the laboratory expert, acquired only by 
painstaking study and entire concentration on that particular phase of 
aviation. 

Due to the ever-changing refinements of design the aim has been to 
present the various parts as representative of the best practice, describing the 
function and operation and, in a brief manner, the construction. In this way 
the aviator learns the fundamentals, so that he is able to instantly com¬ 
prehend the operation of any advanced design which he may later 
encounter. 

A word may be said on bore and stroke ratio. While nothing fixed, 
definite and exact may be stated on the proper proportion of bore to stroke, 
it is clear that an engine with a short stroke will run at high speed smoothly 
but is of poor efficiency at low speeds. When the stroke is much longer than 
the diameter of the cylinder bore, the reverse is true. A bore of 5 inches and 
a stroke of 8 inches is considered a long stroke ratio, 4" x 5" a short stroke. 
Since both ratios have their disadvantages there is no agreement of opinion 
among designers; thus in seven representative types of aviation motors the 
following ratios are found: 4x5, 4x5^, 4x6, 4*4x5, 4^x5, 5x6*4, 5x7. Among 
foreign motors the average is a stroke 1.2 times the bore dimension. The 
general trend in motor design is steadily leaning toward the short stroke, or 
high speed engine, and recent calculations make it appear that the practice 
of restraining piston speed to 1,000 feet per minute will be abandoned. 

A few representative types of multi-cylinder engines will now be briefly 
considered. 


79 


80 


Practical Aviation 



The upper half of the crank case of an 8- cylinder, V-motor is here revealed. The student at the left is holding a piston, and the instructor, in cen¬ 
ter, is pointing to one of the tie-rods, by means of which the cylinders are bolted to the crank case 







V-Type Motors 


81 



Figure 67a—Part section view of 8 -cylinder Figure 6 7b—Part section view of same mo- 

V-motor tor from the front 

V-TYPE MOTORS 

The salient advantages of increasing the number of cylinders in aviation 
engines are, briefly, high speed with decreased vibration, flexibility and quick 
operation, overlapping power strokes and lighter reciprocating parts. The 
addition of more cylinders to the vertical type of motor is impracticable be¬ 
cause this would require a length too great for the fuselage and a much 
stronger and heavier crank shaft; the best solution is therefore found in two 
sets of cylinders inclined inward at an angle, thus producing a motor of same 
length but increased power, or the V-type motor. 

8-CYLINDER V-MOTOR 

The standard Curtiss engine is shown in part section in Figures 67a and 67b. 
It will be noticed that the length of the motor and crank shaft is practically 
the same as in a 4-cylinder engine, and the additions are merely another set of 
cylinders and connecting rods. 

In this engine the cylinders are set at an angle of 90 degrees, or one-half 
the firing distance of the 4-cylinder engine. That is, in this V-type motor the 
power impulses occur every 90 degrees instead of 180 degrees. In the Curtiss 
OX, or 90 horsepower engine, widely used in training machines, the cylinders 
have 4-inch bore and 5-inch stroke, is normally run at 1400 revolutions per 
minute (r. p. m.) and weighs 390 pounds complete. 

The main difference between the 8-cylinder V-motor and the 4-cylinder vertical, is 
the arrangement of the connecting rod; it is common practice to have two rods attached 
to the same crank throw. This is accomplished, (a) by staggering the cylinders and 
having the connecting rods attached side by side to the same crankpin, or (b) the lower 
end of the connecting rod is forked just above the crank shaft bearing, and the rod from 
the cylinder opposite connected to the crank shaft bushing (at a right angle) between 
the fork. 

The firing order is generally the same as in a 4-cylinder motor, except that the 
explosions occur alternately in each set of cylinders. 

12-CYLINDER V-MOTOR 

The development of the multi-cylinder engine to 12 cylinders responded 
to the demand for more power. In V form, it possesses the same advantages 
of arrangement and lightness of weight as the 8-cylinder, and obviously 
reduces vibration still further. That is, where the 8-cylinder engine has four 
power impulses per revolution, the 12-cylinder motor gives six explosions 
per revolution. 

The usual practice has been to set the cylinders at a 60 degree angle, but the latest 
design favors an angle of 45 degrees. 




















































































































































82 


Practical Aviation 



Figure 68—Cross section of a 12-cyl¬ 
inder engine, illustrating many 
features of advanced design 


THE LIBERTY MOTOR 


Details of the general construction of the Liberty motor have been given in an 
authorized statement issued by the War Department, extracts from which follow: 

CYLINDERS 

The cylinders follow the practice used in the German Mercedes, English Rolls 
Royce, French Lorraine Dietrich and Italian Isotta Fraschini. The cylinders are made 
of steel inner shells, surrounded by pressed steel water jackets. (This construction is 
clearly shown in Figure 68, a cross section of a Renault engine.) The valve cages are 
drop-forged, welded into the cylinder head; the principal departure from European 
practice is in the location of the holding down flange, which is several inches above the 
mouth of the cylinder. 

CAMSHAFT AND VALVE MECHANISM 

The design of the cam and valve mechanism is based on the Mercedes, but im¬ 
proved for automatic lubrication without wasting oil. Figure 68 illustrates a good ex¬ 
ample of the type, which has been described in detail on page 66. The camshaft drive 
is of the Hall-Scott type. 

ANGLE BETWEEN CYLINDERS 

The included angle between cylinders of the Liberty motor is forty-five degrees, 
or similar to the illustration Figure 68. 

The general practice in 12-cylinder engines has been to set the cylinders at sixty 
degrees, but by lessening the angle each row of cylinders is brought nearer the vertical 
and closer together, saving width and head resistance, reducing vibration and giving 
greater strength to the crank case. 












































The Liberty Motor 


83 


PISTONS AND CONNECTING RODS 

Hall-Scott design has been followed for Liberty motor pistons; these are similar 
in type to those shown in the drawing on the opposite page. The connecting rods are 
of the straddle or forked type, the fork being just above the bearing at the crank shaft end. 


CRANK SHAFT AND CRANK CASE 

Standard 12-cylinder engine practice is followed, except as to modifications in the 
oiling system. 


IGNITION 

A specially designed Delco ignition system is used. 


LUBRICATION 

The first system of lubrication followed the German practice of using one pump to 
keep the crank case empty, delivering into an outside reservoir, and another pump to 
force oil under pressure to the main crank shaft bearings. This lubrication system also 
followed the German practice in allowing the overflow in the main bearings to travel 
out the face of the crank cheeks to a scupper, which collected this excess for crankpin 
lubrication. This is very economical in the use of oil and is still the standard German 
practice. 

The present system is similar to the first practice, except that the oil, while under 
pressure, is not only fed to main bearings, but through holes inside of crank cheeks to 
crankpins, instead of feeding these crankpins through scuppers. The difference between 
the two oiling systems consists of carrying oil for the crankpins through a hole inside 
the crank cheek, instead of up the outside face of the crank cheek. 


CARBURETOR 


The carburetor is a Zenith development. The compound nozzle principle of the 
Zenith and the constructional details are described on pages 68 and 69. 


BORE AND STROKE 

The bore and stroke of the Liberty engine is 5x7 inches. 

The first Liberty motor was an eight-cylinder model, delivered to the Bureau of Standards July 3, 1917. 
The eight-cylinder model, however, was never put into production, as advices from France indicated that 
demands for increased power would make the eight-cylinder model obsolete before it could be produced. 






84 


Practical Aviation 



A 20-cylinder Anzani motor, built for transatlantic flight, under examination by student mechanics 

















Rotary Engines 


Figure 69 a — General view of nine-cylinder Figure 69 b — Section view of rotary 

rotary engine engine cylinder and crank case 

ROTARY ENGINES 

The principal claim advocated for rotary motors is that the design makes 
for light weight. It has been observed, however, that the rotating feature 
has little to do with this advantage, for the weight would not be perceptibly 
increased if the cylinders were stationary and the crank shaft revolved. Set- 
cing cylinders radially from a crank case of a size not much larger than that 
which one cylinder would require is an obvious weight saving. The absence 
of reciprocating parts aids smooth running and the full practicability of air 
cooling is an added advantage. The head resistance is a disadvantage, and 
the loss of power (estimated at 7 per cent) in driving the cylinders around 
the shaft, and the difficulty of securing high compression, further handicap 
this design. 

GNOME ENGINE 

The Figures 69a and 69b show the famous Gnome engine with nine radial 
cylinders. The explosions occur in each alternate cylinder as the engine revolves, 
the odd number thus securing a uniform period of explosion. The cylinders, 
the construction of which is shown in section in Figure 69b, are machined from 
solid 6-inch steel bars, 11 inches in length, weighing less than 100 pounds. 

The operation of the engine is as follows: 

Vaporized gasoline is forced into the crank case through the jet F (Figure 69b) entering 
the cylinder through the holes A, B, when the piston is at the lowest point. As the piston 
ascends it covers the port and the gas is compressed and fired in the usual manner. The 
large valve in the cylinder head is the exhaust, operated by a cam and rod. Lubricating oil 
enters at C on the stationary crank shaft, passing to the stationary crankpin D and flooding 
the bearings E. A portion of the oil which lubricates the crankpins is thrown by centrifugal 
force through the connecting rod tubes and in the same way oils the piston pins and cylin¬ 
ders. Additional lubrication of the cylinders is secured by oil which is thrown through 
crank case holes. 

In Figure 69a the engine is shown with the crank case cover removed, reveal¬ 
ing the cams and gears. One of the nine holes in the crankpin, through which oil 
is fed to the nine cams, is indicated at A. The cam rollers, one of which is shown 
at B, carry oil over the surface of the cam, surplus oil feeding through the guides 
C of the valve rods, through the ball joint D and hollow rod E to the pin F. A 
groove on the valve lever carries the lubrication to the lever bearing G. 

Other aviation engines of the rotary type include the Anzani, Le Phone and Clerget, constructed with 
varying number of cylinders up to fourteen. 

































































86 


Practical Aviation 



Figure 70 —The proper method of swinging the propeller 


STARTING THE ENGINE 

PREPARATORY 

The ground selected should be firm so that the foot will not slip when the propeller 
is swung. The blocks are then placed in front of the wheels with the cords laid toward 
the wing tips. A mechanician takes his place at each wing tip, grasping the bottom of 
the outer strut to steady the airplane when the engine is running; they pull the blocks 
away when the pilot signals he is ready to start. Two or more mechanicians take their 
places at the tail end of the fuselage to hold it down while the engine is running. 

SWITCH OFF 

The ignition switch must be in the “off” position before any attempt is made to 
swing the propeller. Many fatal accidents have resulted from carelessness on this point. 

With engines of the rotary type it is often necessary to prime the cylinders by 
squirting gasoline through each exhaust valve. Two things are to be remembered in 
this connection: The squirt can must be clean and the ignition switch off. 

GASOLINE ON AND AIR CLOSED 

The pilot ascertains that the gasoline is on and the air intake almost closed, so 
the mixture may be rich for the first few explosions. 

ROTATION OF PROPELLER 

The propeller is swung with the ignition switch off to fill the cylinders with gas. 

CONTACT 

The mechanician calls “contact” at this juncture, whereupon the pilot throws the 
ignition switch on, and replies “contact.” 

SWINGING PROPELLER 

The propeller is grasped as shown in Figure 70. Note particularly the position of 
the feet, shown in plain view at the lower right of the drawing. One good downward 
swing of the propeller is made and the mechanician immediately stands clear. If the 
engine fails to start the mechanician calls for “switch off” and repeats the same operation. 

Once the propeller has been given its downward swing, the mechanician must stand 
clear immediately, as the possibility of a backfire from the engine is great and the back¬ 
ward swing of the propeller may result in a fatal accident. The illustration, Figure 70, 
should be carefully studied, with particular reference to keeping the feet apart and in a 
position where the body will naturally swing away with the downward pull. 



























































Starting the Motor and Fuel Conservation 


87 


SIGNALS 

The following procedure is standard with the Royal Flying Corps. 

1. The pilot ascertains from the rigger and the mechanician that everything is correct, immediately 
after entering the machine. 

2. Mechanician—“Switch off?” 

3. Pilot—’“Switch off.” 

4. Mechanician—'“Gas on—air closed?” 

5. Pilot—“Gas on—air closed.” 

6. The mechanician rotates the propeller to fill the cylinders with gas. 

7. Mechanician—“Contact?” 

8. Pilot—-“Contact.” 

9. The Mechanician swings the propeller and stands clear. The engine runs for a few minutes until 
the pilot is assured that the motor is in good working order. 

10. Pilot waves hand from side to side. 

11. Mechanicians pull blocks away from wheels. 

12. Pilot looks at aviation mechanician or senior non-com, who ascertains if all is clear ahead and above 
for the ascent. He indicates all clear by saluting. 

13. Pilot waves hand in fore and aft direction. This is the signal to start and all stand clear instantly, 
the mechanicians at the tail letting go immediately. 

SELF STARTERS 

There are two methods of cranking aviation engines by starting systems 
employing compressed air. One turns the crank shaft by means of an air 
motor and the other admits compressed air to the cylinders, forcing the piston 
down by pressure and thus turning the motor over. In the latter case, air 
for the system is supplied to a reservoir by an air pump driven by the engine 
and, when needed, enters the top of the cylinders in their proper firing order 
by means of check valves which open inward only and close by explosive 
pressure once the engine is running. 

Developments of the electric starters familiar to all automobilists are 
also being employed on aviation engines. These are of the storage battery 
type with the current generated by the engine when running and stored for 
use until needed. The motor in this instance is turned over when electrical 
communication is made between the storage battery and the motor-generator 
unit, which then acts as a motor and turns the engine over by means of 
gearing to the crank shaft. 

FUEL CONSERVATION IN FLIGHT 

A final word may well be added before turning to the aspects of actual 
flight. When flying, the pilot must bear in mind that the maximum speed of 
the plane is not its most efficient flight speed, and driving the machine at 
full power must not become an habitual practice. The aviator soon learns by 
experience the range of speed of his machine and upon this knowledge must 
base his calculations for long flights, so his fuel may be properly conserved 
for the task in hand. 

To illustrate, a given motor may be assumed to develop 90 H.P. at 
1300 r.p.m. and consume 1-10 gal. of gasoline per horsepower hour, or 9 gal¬ 
lons per hour. If the gasoline tank holds 18 gallons and the speed at 
1300 r.p.m. is 80 miles per hour, the duration of flight will be 2 hours, or 160 
miles. If then, the number of revolutions is reduced to a point where the 
fuel consumption is one-half (at a speed, say, of 60 m.p.h.) the fuel will last 
twice as long, or 4 hours, and the distance covered will be 

60 m.p.h. x 4 hrs. = 240 miles 

as against 160 miles at the greater speed. 

When flying at high altitudes, 10,000 feet or more, motor troubles increase. The 
explosive mixture changes in character, due to the decreased density of the air supplied 
to the carburetor. Lessened supply of air results in increased richness of mixture and, 
disregarding factors of motor design and construction, the amount of power obtained 
will vary with the changes in the proportions of the gasoline vapor. Increased air in the 
mixture means fuel economy, but lessened power. With a rich mixture, on the other 
hand, though the power curve rises, the motor and its parts overheat, delicate adjust¬ 
ments are thrown out and carbon deposits appear in the cylinders. The adjustment of 
the gas mixture is therefore of importance, the normal ratio for aviation engines being 
one part of gasoline to 9 to 20 parts of .air. 


J * 






88 


Practical Aviation 



(c) Committee on Public Information. 

Student aviators of the Signal Corps, U. S. A., learning in the ground school how valves 

are adjusted and ignition timed on aeronautic motors 













Motor Cautions and Trouble Chart 


89 


IMPORTANT DON’TS 

Don’t forget to inspect the motor thoroughly before starting. 

Don’t try to start without oil, water, or gasoline; all three are vital. 

Don’t forget to see that the radiator is full of water. 

Don’t get dirt or water into the oil. 

Don’t get dirt or water into the gasoline. 

Don’t forget to oil all exposed working parts. 

Don’t try to start without retarding the magneto; a serious accident may 
result. 

Don’t try to start without turning on the switch. 

Don’t start the motor with throttle wide open. 

Don’t run the motor idle too long; it is not only wasteful but harmful. 

Don’t forget to watch the lubrication ; it is most essential. 

Don't forget that the propeller is the business end of the motor; treat it 
with profound respect—especially when it is in motion. 

Don’t cut off the ignition suddenly when the motor is hot; allow it to idle 
for a few minutes at low speed before turning off the switch. This insures 
the forced circulation of the water till the cylinder walls have cooled con¬ 
siderably and also allows the valves to cool, preventing possible warping. 

Don’t fail to study the trouble chart before you molest a thing about the 
motor, if you have trouble. 

Don’t develop that destructive disease known as tinkeritis; when the 
motor is working all right, let it alone. 

Don’t forget a daily inspection of all bolts and nuts. Keep them well 
tightened. 

Don’t fail to stop your motor instantly upon detecting a knock, a grind, 
or other noise foreign to perfect operation. It may mean the difference be¬ 
tween saving or ruining the motor. 

THE TROUBLE CHART 

Based on Curtiss engines, this chart has been prepared to outline in a 
simple manner the various troubles that interfere with the efficient action of 
aeronautical motors. 

Defects that may develop are tabulated for ready reference, and opposite 
the part affected the various conditions are found under a heading that de¬ 
notes the main trouble to which the others are contributing causes. 

The various symptoms denoting the individual troubles outlined are given 
to facilitate their recognition in a positive manner. Brief note is also made of 
the remedies for the restoration of the defective part or condition. 

It is apparent that a chart of this kind is intended merely as a guide, and 
it is a compilation of practically all the known troubles that may materialize 
in gas-engine operation. While most of the defects outlined are common 
enough to warrant suspicion, all will never exist in an engine at the same 
time; and it will be necessary to make a systematic search for such of those 
as do exist, and by the process of elimination locate the offending part. 

To use the chart advantageously it is necessary to know and recognize 
easily one main trouble. For example, if the motor is skipping, look for 
possible troubles under the heading “Skipping.” If the motor fails to develop 
power, the trouble will undoubtedly be found under “Lost Power and Over¬ 
heating.” 

It is assumed in all cases that the trouble exists in the power plant or its 
components, and not in the auxiliary members of the ignition. In many in¬ 
stances, however, the seat of trouble will be traced to these latter members. 



90 


Practical Aviation 


SKIPPING OR IRREGULAR OPERATION 




Part at Fault 

Trouble 

Effect 

Remedy 

Spark plug 

Loose binding at post 

Leak in threads 

Defective gasket 

Cracked insulator 

Points too close 

Points too far apart 

Carbon deposit 

Plug too long 

l 

No spark 

Lbw compression 

Low compression 
Short-circuit 

No' spark 

No spark 

No spark 

Pre-ignition 

Tighten terminal 

Screw down tighter 

Replace with new plug 
Replace with new plug 

Set points apart 

Set points closer 

Clean off points and plug 
Change plug 

Combustion chamber 

Carbon deposit 

Pre-ignition 

Remove carbon 

Piston head 

Carbon deposit 

Crack or blowhole (rare) 

Pre-ignition 

Pre-ignition 

Remove carbon 

Replace with new 

Valve head 

Warped or pitted on seat 

Poor mixture 

Low compression 

True up in lathe and grind 
to seat 

Replace with new 

Valve stem 

Binds in guide sticks 

Irregular valve action 

Clean guide 

Straighten stem 

Oil 

Valve spring 

Weakened or broken 

Irregular valve action 

Replace' with new 

Exhaust valve seat 

Scored or warped 

Dirty or covered with 
scale 

Valve will not close 

Poor mixture 

Poor compression 

Use reseat reamer 

Clean off and grind to seat 

Exhaust valve-stem guide 

Warped or carbonized 

Worn guide 

t . 

Valve stem; sticks 

Low compression 

Poor seating 

Poor mixture 

Clean guide or new guide 

Valve-stem clearance 

Too little 

Too much 

Valve will not shut 

Valve "opens late and closes 
early 

Set inlet gap 0.010 

Set exh. gap 0.010 

Camshaft bearing 

Looseness or wear 

V 

Valves' mistimed or valve 
lift short 

Replace with new bushing 

Cam 

Worn contour 

/MU ' ’ 

Valve lift short 

Valves mistimed 

Replace with new cam¬ 
shaft 

Timing gear 

Not properly , meshed 

Loose on shaft 

Worn or broken tooth 

Valves mistimed 

Valves do not act 

Time properly 

Fasten to shaft with key 
Replace with new gear 

Cam-follower guide 

Loose on engine base 

Lock pin sheared off 

Worn in bore 

Oil leaks 

Poor valve action 

Fasten securely 

New pin 

New guide or bushing 

Cam follower 

1 

Loose in guide 

Valves mistimed 

Oil leaks 

Replace with new guide or 
bushing 

Inlet valve 

Closes late 

Opens early 

Blowback in carburetor 

Time properly 

Inlet-valve seat 

Warped or pitted 

Does not seat properly 
Carbon grain under seat 

Blowback in" carburetor 

Low compression 

Use reseat reamer 

Clean off and grind to seat 

Inlet-valve stem guide 

Worn 

Poor mixture 

Low compression 

Bush or replace with new 
guide 

Carburetor 

Weak mixture 

Blowback in carburetor 

Adjust carburetor for richer 
mixture 

Gas manifold pipe 

Leak at joints 

Defective gasket 

Crack or blowhole 

Poor mixture 

Poor mixture 

Poor mixture 

Stop all leaks 

Replace with new 

Solder blowhole 

Piston 

Walls scored 

Poor suction and leak of 
gas 

Smooth up 

Piston rings 

• 

Loss of spring 

Loose in grooves 

Worn or broken 

Slots in line 

Poor suction and leak of 
gas 

Poor compression 

Been rings or replace with 
new 

Loosen rings on piston 

Cylinder wall 

Scored by wristpin 

Scored by lack of oil 

Poor suction and leak of 
gas 

Poor compression 

Lap in cylinder 

Or new cylinder 

Valve-spring collar key 

Broken 

Release spring 

No valve action 

Replace with new key 








































































































The Trouble Chart 


91 


LOST POWER AND OVERHEATING 


Part at Fault 

Trouble 

Effect 

Remedy 

Manifold connections 

Poor mixture in one set of 
cylinders with good mix¬ 
ture in other set 

Surging or pulsating 

Tighten connections; put in 
new gaskets 

Water-pipe joint 

Loose 

Defective gasket 

Loss of \/ater and over¬ 
heating 

1 

Tighten bolts or replace 
with new connection 

Spark plug 

Loose in threads 

Defective gasket 

Poor compression and over¬ 
heating 

(See Spark Plug under 
“Skipping”) 

Screw down tight 

Replace with new 

Combustion chamber 

Crack or blowhole 
Roughness 

Carbon deposit 

Poor compression 
Pre-ignition 

Pre-ignition 

Rill by welding or replace 
with new 

Smooth up 

Remove carbon 

Valve head 

Warped, scored, or pitted 
Carbonized or covered with 
scale 

Poor compression 

True up in lathe and grind 
to seat 

Scrape off smooth with 
emery cloth 

Valve seat 

Warped or pitted 
Carbonized or covered with 
scale 

Poor compression or blow- 
back 

Jse reseat reamer 

Clean off and grind to seat 

Piston rings 

/ 

Loss of spring 

Loose in groove 

Worn or broken 

Slots in line 

Poor suction, leak of gas, 
and over-heating 

Poor compression 

Peen rings or replace with 
new 

Loosen rings on piston 

Piston rings 

Broken because too tight 
Insufficient opening 

Scored cylinder walls, over¬ 
heating in sump pan, and 
poor compression 

Replace scored cylinder if 
groove is deep; use new 
rings 

Wristpin 

Loose 

Scored cylinder 

Poor compression 

Fasten securely 

Replace scored cylinder if 
groove is deep 

Piston head 

Carbon deposit 

Crack or blowhole (rare) 

Pre-ignition 

Poor compression 

Remove carbon 

Replace with new 

Piston 

Binds in cylinder 

Walls scored or worn out 
of round 

Overheating 

Lap off excess metal 

Replace with new 

Cylinder wall 

Scored 

Poor lubrication causes 
friction 

Poor compression and over¬ 
heating 

Replace with new 

Lap in cylinder 

Repair oiling system 

Camshaft 

Drive gear 

Loose on shaft 

Not properly meshed 

Worn or broken teeth 

Irregular valve action 

Fasten to shaft 

Time properly 

Replace with new 

Crank shaft 

Scored or rough on jour¬ 
nals 

Sprung 

Overheating 

Overheating 

Smooth up 

Straighten 

Crankpin 

Bearings and main bear¬ 
ings 

Adjusted too tight 

Defective oiling 

Overheating 

Adjust to running clearance 

Clean out oil holes 

Oil sump 

Insufficient oiling 

Poor oil 

Dirty oil 

Overheating and burned- 
out bearings 

Replenish supply 

Use best oil—Mobile “A” 
recommended 

Wash with kerosene 

Replace with new oil 

Water space and water 
pipes 

Clogged with sediment or 
scale 

Overheating 

Dissolve and remove for¬ 
eign material 

Radiator hose 

Layer of hose obstructs 
opening 

Overheating 

Refit or replace with new 

Water pump 

Impeller loose on shaft 
Dirty 

Broken 

Overheating 

Fasten to shaft 

Clean 

Replace with new 





























































































92 


Practical Aviation 


NOISY OPERATION 


Part at Fault 

Trouble 

Effect 

Remedy 

Spark plug 

Leakage 

Hissing 

Screw down tighter 

Replace with new 

Cylinder wall 

Scored 

Knocking 

Smooth up or replace 
with new 

Manifold pipe joints 

Leakage 

Defective gaskets 

Sharp hissing 

Tighten bolts 

Replace with new 

Combustion chamber 

Carbon deposit 

Knocking 

Remove carbon 

Cylinder casting 

Retaining bolts loose 

Sharp metallic knock 

Tighten bolts 

Cam 

Worn contour 

Metallic knock 

Replace with new 

Piston head 

Carbon deposit 

Knock 

Remove carbon 

Wristpin 

Loose in piston 

Worn 

Dull metallic knock 

Replace or bush 

Connecting rod 

Worn at wristpin or crank 
shaft 

Sideplay in piston 

Distinct knock 

Adjust or replace 

Scrape and fit and oil 

Main crank shaft bearing 

Loose 

Defective lubrication 

Metallic knock 

Squeak 

Fit caps close to shaft 

Clean out oil holes and oil 

Connecting-rod bearings 

Loose 

Excessive play 

Binding 

Intermittent metallic knock 
Knock and squeak 

Refit 

Reline 

Connecting-rod bolts 
Main-bearing bolts 

Loose 

Stripped threads 

Sharp knock 

Tighten 

Replace bolts 

Lower half crank case 
bolts 

Loose 

Stripped threads 

Knock and rattle 

Tighten 

New bolts 

Water jacket 

Covered with scale 

Clogged with dirt 

Knock caused by overheat¬ 
ing 

Dissolve scale and flush 
out water space with 
water under pressure 

Timing gears 

Loose 

Worn or broken teeth 
Meshed too deeply 

Metallic knock 

Rattle 

Grinding 

Fasten to shaft 

Replace with new gear 

Camshaft bearing 

Loose or worn 

Slight knock 

Replace with new 

Inlet-valve seat 

Warped or pitted 

Dirty 

Rattle 

Poor compression 

Blowback 

Use reseat reamer 

Clean off and grind to seat 

Inlet-valve spring 

Weak or broken 

Blowback in carburetor 

Replace with new 

Inlet valve 

Closes late 

Opens early 

Blowback in carburetor 

Time properly 

Valve-stem guide 

Worn or loose 

Rattle or click 

Replace with new guide 

Cam-follower guide 

Loose 

Rattle or click 

Replace with new guide 

Valve-stem clearance 

Too much 

Too little 

Click 

Blowback in carburetor 

Set inlet gap 0.010 

Set exh. gap 0.010 

Push-rod retention 
stirrups 

Nuts loose 

Rattle 

Blowback in carburetor 

Tighten nuts 

Crank case gaskets 

Leak 

Oil leak 

Tighten bolts 

Replace with new 

Cylinder or piston 

No oil 

Poor oil 

Grinding and sharp knock 

Repair oil system 

Use best oil 

Piston 

Binding in cylinder 

Worn oval, causing side 
slap 

Grind or dull squeak 

Dull hammer 

Lap off excess metal 

Replace with new 

Oil sump 

Insufficient oil 

Poor oil 

Grind and squeak in all 
bearings 

Replenish with best oil 

Piston rings 

Defective oiling 

Squeak, hiss, grind 

Replace with new ring 

Repair oil system 

Crank shaft 

Defective oiling 

Squeak 

Clean out oil holes 

Use best oil 

Repair oil system 

Engine base 

Loose on frame 

Dull pound 

Tighten bolts 









































































































































Practical Aviation 


93 


REVIEW QUIZ 

Types of Motors, Operation and Care of Engines 

1. State the relation to efficiency of an engine with a short stroke 

running at high speed. At low speed. 

2. Name four advantages gained by increasing the number of cylinders 

in aviation engines. 

3. Why is the V construction best for multi-cylindered engines? 

4. Explain how the length of the crank shaft of an 8-cylinder V-motor 

is practically the same as that of a 4-cylinder vertical engine. 

5. Describe two methods of attaching connecting rods in pairs to one 

crank throw. 

6. Give the number of power impulses per revolution of a 12-cylinder 

motor. 

7. State and weigh the respective values of the advantages and dis¬ 

advantages of rotary engines. 

8. Briefly describe the operations of the Gnome engine. 

9. State the positions and duties assigned to five mechanicians required 

when an airplane prepares for flight. 

10. Explain how the propeller should be grasped for cranking, with 

particular reference to first and second positions of the feet. 

11. If the engine fails to start what action is required before repeating 

the operation? 

12. Give the full set of signals which governs the acts of pilot and 

mechanician during preparation for immediate flight. 

13. How does a compressed air self-starter turn the motor over? 

14. By an example, explain how fuel may be conserved for long flights. 

15. In what way does altitude affect the amount of power secured from 

the engine? 

16. Give twelve important precautionary acts of motor inspection before 

starting. 

17. When the explosive charge in cylinders ignites too soon what parts 

should be examined? Suggest two remedies when the fault is 
located. 

18. Name five parts which should be examined if the motor is over¬ 

heating. 

19. When a knock or a grind is detected what should be done instantly? 

20. Describe the character of the noise which warns of a defective con¬ 

necting rod bearing. 




94 


Practical Aviation 


CHAPTER ANALYSIS 

Instruments and Equipment for Flight 

AVIATOR’S EQUIPMENT: 

(a) Clothing. 

(b) Goggles. 

(c) Watch. 

(d) Safety Belt. 

AIRPLANE INSTRUMENTS: 

(a) Scope and Usefulness. 

(b) Cockpit Arrangement. 

(c) Gauges. 

(d) Compass. 

(e) Barometer or Altimeter. 

(f) Tachometer. 

(g) Angle of Incidence Indicator. 

(h) Inclinometer. 

( i) Radiator Temperature Indicator. 

(j) Drift Meter. 

(k) Air Speed Meter. 

(l) Banking Indicator. 




CHAPTER X 


Instruments and Equipment for Flight 


Before beginning consideration of actual flight, a preliminary survey of the 
aviator’s equipment and aids is advisable. These consist of his clothing and 
accessories and the instruments which aid navigation of the air. Many argu¬ 
ments are advanced for the method of instruction by which the pilot acquires 
a sense of “feel” without dependence upon mechanical devices, but while 
this instinctive knowledge is essential, intelligent use of the instruments 
undoubtedly increases the aviator’s efficiency. 

Clothing —A warm coat is a necessity, for even in summer it is cold at 
high altitudes. In winter a fur lining is advisable; in ordinary moderate 
weather the service uniform covered by a leather coat is sufficient. Pockets 
without flaps, closing by an elastic band, should be of generous size so that 
papers may be easily put away with one hand. Warm socks are essential 
and soft boots or puttees without straps should be worn with the riding 
breeches. Fleece-lined soft leather gauntlets, allowing easy freedom of fingers 
and wrists, are the proper protection for the hands. A padded helmet is a 
necessity. The aim in selecting clothing is to provide flexibility of movement 
and protection from the cold with the minimum of straps and strings to 
catch on the obstructions within the cockpit. Above all, clothing must be 
comfortable. 

Goggles —As a protection from the wind, even though the airplane be 
provided with a wind shield, goggles should be used to take the strain off the 
eyes. Glass lenses should not be used; they should be made of colorless 
celluloid with a green shade at the top and bound by a stiff rubber rim 
shaped to conform to the face. A small piece of chamois should be carried 
to wipe off the flying oil. 

Watch —An accurate timepiece with a wrist strap is essential to the 
military aviator. 

Safety Belt —Under no circumstances should the aviator venture aloft 
without his safety belt adjusted. This device consists of a wide web of heavy 
webbing with a quick detachable locking device. The belt should be securely 
adjusted with the stress coming at the thighs. 

95 


96 


Practical Aviation 



Figure 71 —General view of a typical airplane cockp 


it 


AIRPLANE INSTRUMENTS 
SCOPE AND USEFULNESS 

As with any class of travel, reaching the destination by air flight requires 
knowledge of position. The aviator obviously must also know the direction 
of his machine toward the horizontal. In or above the clouds, out of sight 
of earth, knowledge of these essentials must be gained through instruments. 
The devices required for air navigation must be compact and rugged, light, 
reliable and accurate. 

GAUGES 

An oil gauge definitely indicates the amount of oil in the crank case, an 
oil-pressure gauge accurately indicating undisturbed flow and the pressure 
in the oil system. The gasoline gauge registers the quantity of gasoline 
available in the tanks, preferably by mechanical means. 

LUMINOUS DIALS 

Paints and compounds which illuminate pointers and figures on instru¬ 
ment dials are now in general use, electric lighting having been largely 
done away with because of the glare and the vibration to which lights are 
subjected. Zinc sulphide combined with radium are the main constituents of 
the most reliable luminous paints. 

COCKPIT ARRANGEMENT 

Wherever practicable, well upholstered seats are provided for aviators 
and in many cases comfort is further promoted by passing heated exhaust 
pipes through the cockpit. Figure 71 shows a typical arrangement of the 
pilot’s seat and dash with air navigation instruments in position of easy 
visibility. 
















Compass, Altimeter and Tachometer 


97 



Figure 72 —A military airplane compass 



Figure 73 —The barometer or altimeter 


COMPASS 

Air navigation, as well as sea, requires the aid of the compass, a device 
which contains a magnetic needle constantly pointing to the magnetic north. 
In the aviation compass illustrated in Figure 72 a compensating attachment 
counteracts stray magnetic influences. The card, or graduated scale, floats 
in a mixture of alcohol contained in the inner bowl, the latter being bedded 
in horsehair, which absorbs vibration. The alcohol varies in proportion to 
water from 45 per cent to almost pure alcohol, the high percentage being 
maintained to prevent freezing at high altitudes. 

BAROMETER OR ALTIMETER 

To indicate the height of the airplane above the earth is the function 
of the instrument illustrated in Figure 73. Essentially, it comprises a vacuum 
chamber which is acted upon by the varying density of the air. The dial is 
adjusted to zero on the ground. Location of the instrument on the airplane 
is of great importance by reason of the possibility of influence by velocity 
pressure. 

TACHOMETER 

This instrument, not illustrated, is in all essentials similar to the speed¬ 
ometer used for automobiles, except that it registers the number of revolu¬ 
tions of the motor. Its importance may be estimated by considering that the 
power delivered by the engine is directly related to its speed of revolution 
and that the speed of its turning may be used to compute the airplane’s 
speed relative to the air. Tachometers are either magnetic or electric, the 
former type consisting of a magnet rotated by a flexible shaft coupled to the 
engine, and the latter comprising a generator, engine driven, electrically con¬ 
nected to an ammeter. With both types the indications are made by a needle 
and graduated arc on the dash. 








98 


Practical Aviation 



(c) Press Ill. Svce. 

The amazing development of aircraft is revealed in this photograph of the nezv Caproni triplane, features of which are the twin \2-cylinder motors and 
~tractor screws with the addition of a pusher propeller behind the nacelle. The wireless generators are located on the struts just 
underneath the engine beds. In the center of the group are the Caproni brothers, builders of the leviathan of the air 













Incidence Indicator and Inclinometer 


99 



Figure 74— Angle of incidence indicator 



Figure 75— An inclinometer Figure 76— Engine temperature meter 

ANGLE OF INCIDENCE INDICATOR 

This device, illustrated in Figure 74, is mounted on a forward strut clear of the 
influence of the propeller and the body. The vane, which remains level when the air¬ 
plane is in motion, has a pointer and indicator graduated in degrees and visible to the 
aviator. The instrument shows the angle between the chord of the wings and the flight 
path. By means of a dry battery and electrical connections the round light bank shown 
is attached. When the flight is level no light shows. A white lamp signals when a dive 
is made at too steep an angle. A red light warns of an angle close to the stalling point. 
A green light indicates the best climbing angle. 

INCLINOMETER 

Two types of inclinometers are illustrated. The spirit-level type shown mounted 
on the dash in Figure 71, is inaccurate in the presence of accelerations and has gen¬ 
erally been superseded by the instrument illustrated in Figure 75. This device registers 
the angle of the airplane with the horizontal, the scale being on a weighted wheel 
which is damped by floating in liquid, which insures sensitiveness and increases 
accuracy. The scale tips forward or backward with the angle of the airplane, the 
dial being mounted on the instrument board in the cockpit. 

RADIATOR TEMPERATURE INDICATOR 

The value of this device, illustrated in Figure 76, is obvious when it is considered 
that great altitudes are attained by airplanes and the necessity of knowing whether the 
motor is getting cold Equally important is knowledge of imminent overheating. The 
instrument is, therefore, designed to register from freezing to boiling. 












100 


Practical Aviation 



Figure 78 —Air speed meter 


Figure 77 —The drift meter 


DRIFT METER 




Figure 79 —Banking indicator 


The purpose of this instrument, shown in Figure 77, is to enable the aviator to 
remain on a given course to his destination, irrespective of drift occasioned by side 
winds. The device comprises a telescope pointing vertically to the earth with hairs 
crossing the field of vision. A scale and pointer indicates the angle of drift in degrees 
and the compass lubber line moves automatically to correct for any existing drift. The 
instrument is widely used for cross-country flight. 


AIR SPEED METER 

This mechanism shows the airplane’s rate of speed relative to the air. It serves to 
correct for the aviator any erroneous impressions which may be gained by his speed 
in relation to the ground, since that speed varies according to whether his airplane is 
flying with or into the wind. It is also useful to indicate excessive gliding speed, 
straightening out from which may stress the machine to dangerous limits. The prin¬ 
ciple of its operation is pressure of wind on a liquid contained in a tube, a lead from 
one end of which is open to the wind. This device is also known by the names, 
manometer and Pitot tube. 


BANKING INDICATOR 

The proper lateral attitude of flight is shown on this instrument by the airplane 
outline on a fixed dial, below which is a bar rotating from the center and controlled by 
a pendulum inside the case. When the indicator bar and the wing outline are parallel, 
as in the illustration, Figure 79, the machine has the proper amount of bank. The pen¬ 
dulum swings outward in proportion to the radius and speed of the turn, and when the 
pilot has not properly banked his airplane the indicator bar will be out of parallel with 
the wing outline on the dial. The pilot then merely operates his controls in the indicated 
direction until the parallel is again registered. The instrument is of special value to 
the aviator at night or in a cloud or fog when human sensibilities are not dependable. 











Practical Aviation 


101 


REVIEW QUIZ 

Instruments and Equipment for Flight 

1. What type of goggles are best and why should a piece of chamois be 

carried? 

2. Is there any occasion when an aviator should make a flight without 

first adjusting his safety belt? 

3. What is the function of the compass? 

4. Why should the altimeter be located in a position where the airplane’s 

velocity will not affect it? 

5. What are the two types of tachometers? 

6. How many electric light signals are given by the angle of incidence 

indicator? 

7. When the flight is level no light shows; which lamp, then, indicates 

best climbing angle? 

8. If a white lamp is flashed by the action of the indicator, what does it 

indicate? 

9. Give the essential difference between two types of inclinometers and 

state what these instruments register. 

10. How does the drift meter indicate and correct the angle of flight in a 

side wind? 

11. Explain how the air speed meter corrects possible erroneous impres¬ 

sions of the velocity of the airplane’s flight. 

12. How is this indicator valuable in showing gliding speed? 

13. Give two other names by which the air speed meter is known. 

14. What is the relative position of indicator bar and wing outline on the 

banking indicator when the airplane is properly banked? 

15. Under what flight conditions is this instrument specially valuable? 






102 


Practical Aviation 


CHAPTER ANALYSIS 

Instruction in Flying 
First Flights and Cross-Country Flights 


INSTRUCTION IN FLYING: 

(a) The Flying Course. 

(b) Junior Military Aviator Tests. 

(c) Flying by Dual Control. 

(d) Flight Instruction by Solo 

Method. 

(e) Military Aviator Course. 

(f) Advanced Flying. 

FIRST FLIGHTS: 

(a) Position for the Start. 

(b) Leaving the Ground. 

(c) Climbing. 

(d) Turning. 

(e) Straightening Out. 

(f) S-Turns. 

(g) Right of Way. 

(h) Meeting an Airplane. 

(i) Overtaking an Airplane. 

(j) Meeting at an Angle. 

(k) Landing Sites. 

(l) Landing. 

(m) Bad Landings. 

CROSS-COUNTRY FLIGHT: 

(a) Equipment. 

(b) Physical Fitness. 

USE OF THE COMPASS: 

(a) The Compass Card. 

(b) Compass Error. 

(c) Variation. 

(d) Deviation. 

(e) Adjusting the Compass. 

(f) Placing the Compass. 

LAYING OFF A COURSE: 

(a) Determining the Steering 
Direction. 


(b) 

Data Required. 

(c) 

Preparing a Diagram 
Wind Factor. 

(d) 

Radius of Action. 

SOME FLIGHT CONSIDERA 

TIONS: 

(a) 

Proper Preparation. 

(b) 

Height. 

(c) 

Air Disturbances. 

(d) 

Lost Bearings. 

(e) 

Landmarks. 

(0 

Time Checking. 

(g) 

Selecting Landings. 

(h) 

Forced Landings. 

(i) 

Pegging Down. 

(j) 

Re-Starting. 

MAP 

READING: 

(a) 

Definition of Terms. 

(b) 

Orienting. 

(c) 

The Scale. 

(d) 

Contours. 

(e) 

Conventional Signs. 

(0 

Map Preparation. 

THE 

FLYING CREW: 

(a) 

The Navigator. 

(b) 

The Pilot. 

(c) 

The Observer. 

(d) 

Motor Engineer. 

(e) 

The Gunner. 

(0 

Radio Operator. 

THE 

REPAIR CREW: 

(a) 

Aviation Mechanician. 

(b) 

Assistant Chief of Crew. 

(c) 

Mechanician Helpers. 






CHAPTER XI 


Instruction in Flying 
First Flights and Gross-Country Flights 

The theory of aviation may now be said to be fully covered and the stu¬ 
dent ready for text on actual flight. If the preceding chapters have been care¬ 
fully studied there is no flight evolution of the airplane which is not entirely 
understandable to the reader. The function and operation of the airplane as a 
whole, and its controlling means as separate and unified parts, will be clear 
without further explanation in the description of the various flight maneuvers. 
One point may well be repeated here, however, to fix the matter clearly in the 
student’s mind. I hat is the results of operation of the stick control and rud¬ 
der, which may be simplified as follows: 

To go down, push the stick control forward. 

To rise, pull it back. 

To tilt to the left, push it left. 

To tilt to the right, push it right. 

To turn left, rudder with left foot. 

To turn right, rudder with right foot. 

Thus it is seen that the movements are the natural ones; for example, if 
the airplane is tilted sideways to the right the natural tendency is to lean left. 
Pulling the stick to the left rights the plane; and so on, each motion being the 
automatic one, so to speak. 

During early stages of flight training the pupil must not hesitate to 
tell the instructor if at any time he feels physically or temperamentally unfit. 
Flying when not mentally inclined for the instruction will quickly ruin an 
aviator’s prospects for later success, and any hesitancy about stating his con¬ 
dition for fear of a “cold feet’’ accusation is not to be tolerated. Aviation in¬ 
structors and students are sympathetic, earnest men; they have no time for 
taunts. 

Acquiring confidence in early stages is a tremendous help; until it is 
acquired the first solo flight should not be attempted; usually, after five hours 
dual-control instruction, the elementary machine may be flown solo. Some 
fifteen or twenty flight hours on various elementary types is generally suf¬ 
ficient, and the faster airplanes may then be used. Take-offs and landings 
should be frequent in practice, for nothing more quickly instills confidence 
than knowledge that the matter of alighting has been mastered. 

In this 1 chapter, the scope of the preliminary training will be considered 
by progressive steps, a survey of the whole subject being given by first defining 
the composition and duties of the flying and repair crews and the tests for 
grading as an aviator. 

103 


104 


Practical Aviation 


INSTRUCTION IN FLYING 

Candidates for instruction in aviation in the U. S. Army are selected from 
the following sources: 

Officers of the line of the Army. 

Enlisted men of the Aviation Section, Signal Corps. 

Civilian aviators, employed as Instructors. 

Civilian aviators, employed to perform flying duties and given the rank 
of Aviator, U. S. Army. 

Officers and enlisted men of the Signal Officers and Signal Enlisted 
Reserve Corps. 


THE FLYING COURSE 

The instruction is divided into definite stages comprising a complete flying- 
course, as follows: 

(a) Preparatory. 

(b) Preliminary. 

(c) Elementary. 

(d) Advanced. 

The preparatory instruction includes all the teaching up to the point 
where the pupil actually takes hold of the controls while the craft is in flight 
through the air. Preliminary training may be defined as the instruction up 
to the point where the student makes a flight alone, making quarter, half or 
full turns. Elementary training is the stage of instruction preliminary to the* 
completion of pilot’s tests. Advanced flying is the next step up to the qualifi¬ 
cation tests as a junior military aviator. 


JUNIOR MILITARY AVIATOR TESTS 

(a) Five figures-8 around pylons, keeping all parts of the machine inside 
of a circle with a radius of 300 feet. 

(b) Climb out of a field 1,200x900 feet and attain 500 feet altitude, keep¬ 
ing all parts of the machine inside of the field during climb. 

(c) Climb 3,000 feet, kill motor, spiral down, changing direction of spiral, 
that is from left to right, and land within 150 feet of a previously designated 
mark. 

(d) Land with dead motor in a field 800x100 feet, assuming the field to 
be surrounded by a 10-foot obstacle. 

(e) From 500 feet altitude, land within 100 feet of a previously desig¬ 
nated point, with a dead motor. 

(f) Cross-country triangular flight of approximately 60 miles without 
landing. 

(g) Straightaway cross-country flight, without landing, of about 90 
miles. 






105 


Flight Instruction Methods 


FLYING BY DUAL CONTROL 


THE AIRPLANE 

A machine of moderate power and slow speed is used, with large surfaces 
for slow landing speed. Dual controls are provided, so that either instructor 
or student can control the craft. 

FIRST STAGE 

1 he student merely observes the operations of the instructor at the be¬ 
ginning. He is given the “feel'’ of the air and taught to gauge, by the air 
pressure against face and body, his speed and flotation for horizontal flight, 
climbing and banking. The machine’s response to the controls is noted and 
their resistance to motion observed. 

SECOND STAGE 

Instruction is given in the operation and management of the controls. 
Horizontal flights are followed by broad, flat turns, quarter, half and full 
circles to right and left, simple, normal landings and take-offs and balancing 
the airplane in the air. Flight through unfavorable, disturbed air is next 
performed, including banking, climbing and gliding, moderate spiral glides 
and straight and spiral volplanes. Landings of various kinds are then taught, 
including normal, slow-speed, pancake and stall landings, and landing in wind. 
The instructor gradually turns over the air controls to the student as the in¬ 
struction progresses, and finally the power controls. Taxying, or maneuvering 
the machine on the ground, is also mastered before the student takes to the 
air alone. 

FLYING ALONE 

Detailed instructions as to the flight course and maneuvers to be per¬ 
formed are given by the instructor before the student flies alone, and the 
altitude is also prescribed. The first flight alone is elementary, being 
restricted to horizontal flight, take-offs and landings on a straight course. 
It is followed by adding circles to right and left, moderate climbs and straight 
glides. Figures eight are made with gradually decreasing radii and steeper 
banking; the turns are then combined with glides and advanced to spiral 
glides. From both straight and spiral glides, landings are then made with 
a dead motor. The instructor watches his pupil closely from an observation 
tower during these flights and corrects all faults observed at the completion 
of the flight. 






106 


Practical Aviation 


FLIGHT INSTRUCTION BY SOLO METHOD 
FIRST STAGE 

The first machine used for this method, practically one of self-training by 
progressive use of selected airplanes, is low powered with small lifting sur¬ 
faces, in fact not intended for use off the ground. The speed of propeller 
revolution is limited by a stop on the engine throttle. The student first learns 
the manipulation of controls from the pilot’s seat, that is, the rudder, elevators 
and balancing planes, or ailerons. He is then taught to “taxi” on the ground, 
using a straightaway course on a broad, flat and hard path, and to acquire 
skill in steering the machine on the ground. 

SECOND STAGE 

The next machine is one of limited power but designed to lift off the 
ground for a height of about two feet, the lift being regulated by the throttle 
of the engine. The limitation of power causes the machine to sink gently 
back on the ground but permits the student to master the operation of the 
elevator. Hops up to 200 feet are made in this way and the handling of 
balancing planes is accurately learned. From then on the machine is regulated 
gradually until straightaway flight is made at heights up to 20 feet, several 
take-offs and landings being required with each flight. 

THIRD STAGE 

The next machine is of an advanced type and in it flights are made at an 
altitude of 50 feet, at which very slight curves are taken along the course. 
Increasing altitudes are attained and these curves are gradually advanced to 
circles, with greater angle of banking for decreased radius or increased speed; 
these are mastered by barely perceptible degrees. Broad figures of eight 
follow and straight and spiral glides under throttled power advance to glides 
without power, or the volplane. Accuracy in landing on a mark and coming 
to rest over a mark are then attained. 

COMBINATION OF TRAINING METHODS 

Where time permits, the best training course is a combination of solo and' 
dual methods, the former to give the student self-reliance and the dual con¬ 
trol instruction to correct any errors acquired in training. 

MILITARY AVIATOR COURSE 

Advanced flying is begun with training designed to perfect judgment in 
landings and the volplane. Difficult conditions are then imposed, the flyer 
being taught to handle his machine near buildings, fences and all classes of 
obstructions, first on the ground and then in the air. He is trained to rise and 
land over imaginary obstacles or over a specified height, indicated by a string 
stretched between two posts and marked by a pennant. He ascends from and 
descends into fields of restricted area, which for safety are marked by chalk 
lines. 

High-powered machines and unfavorable weather are selected and sharp turns, 
steep banks, spiral glides and difficult landings are practiced. The instruction is mainly- 
designed to give the pilot confidence in his abilities and to impress upon him caution 
and thoroughness. 

The elementary observer’s course consists of progressive flights at increasing 
altitudes and under varying conditions of visibility, from clear weather to foul. Visi¬ 
bility tests with naked eye and field glasses of various powers are made, followed by 
instruction flights in reconnaissance and navigation of the air. Short cross-country 
flights in preparation for junior military aviator tests are then in order. 

These tests complete the training as a military pilot; further development is 
acquired by training on various types up to super-planes and high speed pursuit planes. 
Expert aviators are required to attain a minimum altitude of 12,000 feet, remain in 
flight for four hours and cover 200 miles, cross-country. 






107 


Instruction in Flying 


ADVANCED FLYING 

1 he advanced work is classified by the Training Department of the Army 
Aviation Schools into special phases as follow:.: 

Excessive use of controls 
Reduced power flights 
Flat glides 
Steep climb 
Banking up to 90° 

Fast landings and take-offs 

Landing across wind 

Stalls, side-slips, tail-slides, loops 

Bad weather; rain 

Water flying 

Night flying 

Altitude flights; duration flights; cross-country flights 
Passenger carrying and low flying 

The course of study and practical work embraces the elements of aeronau¬ 
tical engineering, use of meteorological and aeronautic instruments; advanced 
meteorology; practical reconnaissance; spotting artillery fire; bomb drop¬ 
ping; principles of aerial combat; wireless telegraphy; gunnery; strategic 
and tactical employment and administrative control of the air squadron. 



Photo Com. Pub. Inf. 

American beginners in France receiving solo instruction on the elementary non-flying machine 





















108 


Practical Aviation 



The heavy bombing plane, or super-plane, here illustrated, carries as many as six men and eight machine guns 




















Duties of Airplane Crews 


109 


THE FLYING CREW 

An airplane’s flying crew is largely governed by the type of machine. 
Small machines of high power, designed either for strategic reconnaissance 
flights or pursuit at high speeds, carry but a single aviator. The two-seater, 
or most common airplane carries an observer or gunner. Aircraft of the 
super-plane class carry from 3 to 15 men, comprising additional duties of 
navigator, gunner, engineer and radio operator. 

THE NAVIGATOR 

Military control and direction of pilot, gunners, bombers, radio operator 
and engineers, as well as the navigation of the machine in flight, is the duty of 
the navigator, usually the senior officer of the crew. 

THE PILOT 

Management of the controls of the airplane while in flight is the duty of 
the pilot. He is also responsible for Anal inspection of the craft before the 
flight is begun, and for the careful completion of any repairs or alterations on 
the machine. Immediately upon return from a flight it is his duty to examine 
minutely all controls, lifting surfaces and braces and supervise all mechanical 
adjustments not included in shop work. 

THE OBSERVER 

Preparation of reconnaissance maps and reports, all observations and 
computations of flight navigation, is the duty of the observer. In combat he 
directs the fire against enemy airplanes and, if on a bombing expedition, 
orders the use of explosive or incendiary bombs according to the objective. 
He is also responsible for the efficiency of the personnel of the crew and the 
materiel. 

MOTOR ENGINEER 

Uninterrupted operation of the motor or motors in flight is the responsi¬ 
bility fixed on the motor engineer. At all times he performs, with the help 
of an assistant, any work necessary to insure the highest operating efficiency 
of the airplane’s engines, and is responsible for all repairs other than those 
required to be made in the machine shop. 

THE GUNNER 

Expertness in the care and operation of machine guns and the construc¬ 
tion and operation of explosive and incendiary bombs is required of the gun¬ 
ner. Range-finding, loading and releasing devices for bombs and telescope 
and air compressor must also be thoroughly mastered. 

RADIO OPERATOR 

Installation of apparatus, assembly and dismantling of radio equipment, 
thorough knowledge of all* codes of army signaling, are qualifications of the 
radio operator. In addition, he is responsible for all communications from 
the airplane and must be familiar with the operation of visual signaling- 
devices, such as the Very pistol, rockets, smoke bombs, etc. 





110 


Practical Aviation 


THE REPAIR CREW 

Two non-commissioned officers and three privates, first class, are gen¬ 
erally assigned to an airplane and are responsible for its care on the ground. 
In the case of small airplanes the repair crew may consist of only three men, 
but the general practice is a crew of five. 

AVIATION MECHANICIAN 

The chief of the repair crew is rated first class sergeant or sergeant, and 
in the U. S. Army is known as Aviation Mechanician. He is responsible for 
the condition of the airplane and its materiel while it is in the hangar; he 
supervises all adjustments, alterations, installations and repairs. All property 
issued for maintenance and all tools and accessories are in his charge, and 
he is responsible for the cleaning and preservation of the craft. 

ASSISTANT CHIEF OF CREW 

Rated as a sergeant or a corporal, the assistant aids the chief and is 
required to be a qualified mechanic capable of discharging all duties of the 
chief of crew. 


MECHANICIAN HELPERS 

The three mechanician helpers, rated as privates, first class, are under the 
orders of the chief of crew and his assistant. They are required to assist in 
adjustments, alterations, removals, installations and repairs, to clean the 
motor and all parts of the airplane fuselage and surfaces, fittings and fixtures, 
wires and cables. It is their duty to keep the hangars clean at all times; to 
replace tools and equipment; to elevate the machine on chocks or jacks when 
in its stall and to cover the motor propellers and cockpit. Hauling gasoline, 
oil and other supplies and assisting in repair work are among their duties. 
When not employed about the machine they are required to be available for 
instruction or duty in the machine and repair shop. 






First Flights 


111 



Figure 80 —An airplane headed into the wind, the position for the start 



Figure 81 —Taxying at the start with wheels on the ground and tail raised 

FIRST FLIGHTS—THE START 

The airplane should be turned directly against the wind, as this position 
aids the initial rise from the ground and makes it easier to maintain balance, 
a difficult matter in a cross wind. 


LEAVING THE GROUND 

The engine should be developing full power for the required thrust before 
the signal is given for the mechanicians to let go. As the airplane starts 
forward along the ground, the tail stabilizer is depressed by moving its control 
forward. This causes the tail to rise from the ground and places the lifting 
surface more horizontal, offering less resistance as rolling speed is acquiiet. 
Figure 81 illustrates this position. When the machine is taxying at a velocity 
equal or greater than the airplane’s low flying speed, the tail control is 
pulled back gently and held. The tail end of the machine then drops and the 
ano-le of incidence of the wings is increased, causing the airplane to rise. 

A minimum distance of 100 yards (covered in 5 to 10 seconds, according to the 
wind) is allowed between the starting point and the rise from the ground. 


CLIMBING . , , , , _ , . i 

The tail control is pulled back slightly and held hxed m the new position, 

further increasing the lifting surface angle of incidence. 1 he motor is then 

accelerated to its proper climbing speed. f . .... , , 

The airplane should be pointed into the wind for the first 200 feet of altitude and 
the student flier should rise at least 100 feet. A landing made from a lesser height is 
valueless for instruction purposes. 















112 


Practical Aviation 



Figure 82 —A turn made too flat Figure 83 —Too steep banking 


TURNING 

Turning with the novice almost invariably reveals one fault, i. e., the 
banking is too steep. This must be corrected before the aviator attempts the 
steep turns. The following general rules will prove useful in learning to turn 
the airplane correctly. 

A good altitude margin should be allowed, so there will be at least 500 feet to 
correct for bumps or side-slips. 

First turns should be very wide and not through more than 180 degrees, or 
half-turn. 

While turning, speed should be kept up to at least level flying speed, and the 
airplane nosed down to its normal gliding angle. If flying speed is lost, the machine 
will side-slip or stall, getting into the cabre, or tail down, position which is dangerous 
to the novice. 

As the natural tendency is to lose height, it is best to turn the airplane against 
the wind at first. 

Aileron and rudder controls should be handled gently and first turns made 
gradual ones. 

Figures 82 and 83 show turns improperly made. A turn too flat causes an out¬ 
ward side-slip, and too steep banking an inward side-slip. Either of these faults 
are perceptible to the aviator by the feel of the wind on his face. During a right 
turn, for instance, a noticeable wind on the opposite, or left, cheek indicates an out¬ 
ward side-slip. This is corrected by gently pushing the stick to the right for more ‘ 
bank or turning the foot bar for less rudder. When the opposite effect on the cheek 
is noticed, more rudder and less bank is required. 

Gradually, turns may be made smaller until a 2^-turn spiral in 1,000 feet is 
accomplished. Turning while volplaning may then be tried. 

In gliding turns the airplane’s nose should be kept below the line of the horizon. 
Climbing turns require the nose of the machine above the horizon. 

STRAIGHTENING OUT 

A few simple rules will serve to teach how to come out of a turn properly. 

Theoretically, the rudder and aileron controls are brought back to central posi¬ 
tions. In many airplanes, however, they must be brought over to the opposite 
bank first and centered when the machine is level. The stick control should be 
moved a trifle sooner than the rudder, and brought past center, being returned to 
central position when the rudder is at center and the airplane at a horizontal level. 

Coming out of a steep turn these control movements are made greater, the stick 
being given a semi-circular action. Special care should be taken that the rudder is 
not swung over opposite too early, for this will throw the nose of the airplane up 
and an inward side-slip will result. 

S-TURNS 

These are a series of descending Figure 8s or S-turns, useful for landing in a 
restricted area. Two rules should be followed. During the entire turn the aviator 
should keep his eye on the landing spot selected and always turn toward that point. 
The turns are made increasingly smaller as the ground is approached for the finai 
glide. 

Turning near the ground should be avoided; speed should be maintained by 
keeping the nose down. 

















Rules of the Air 


113 



Figure 84 —The overtaking airplane steers Figure 85 {Upper)—Distance for passing in 
clear about 100 yards of the slower opposite directions 

machine ahead and avoids the Figure 86 {Lower)—How an airplane gives 
disturbed air of the backwash way to one met on its right 

RIGHT OF WAY IN THE AIR 

The student aviator should acquaint himself with the air rules of the 
flying school to which he is assigned. The courses are usually prescribed and 
the direction of circuits and pylon markings clearly stated. While slight 
variations may be encountered at various flying fields, the following general 
rules are almost universally observed: 

OVERTAKING AN AIRPLANE 

The faster machine coming from the rear maintains the minimum distance, 100 
yards, by steering clear, care being taken that the overtaking machine is not brought 
within the zone of influence of the backwash, for in the disturbed air rough going 
will be encountered. See Figure 84. 

MEETING AN AIRPLANE 

When an airplane is encountered coming in the opposite direction, both machines 
keep to the right and pass at a minimum distance of 100 yards. See Figure 85. 

MEETING AT AN ANGLE 

In a situation such as illustrated in Figure 86, where two airplanes approach at 
an angle, the aviator who finds the other machine on his right gives way. 

LANDING SITES 

The United States Army requires of a flying field for testing aviators a minimum size of 800 by 100 
feet. The general area of a field is about 9 acres, 200 yards square. Area allowances are added for 
obstacles, proportionately based on the obstacle’s height, 12 times the height being added to the area, or 
12 feet of field depth added for every foot of obstacle height. 

The above regulation applies only to machines of slow landing speed. When fast airplanes are 
used, the 200-yard depth is added to as follows: 40 m.p.h., 60 yards; 45 m.p.h., 120 yards; 50 m.p.h., 
360 yards; 55-60 m.p.h., 960 yards. These dimensions are based on landing and taking off against the wind. 

Plowed fields, soft ground and ditches are dangerous to the inexperienced aviator and should be, 
avoided as landing places. 

Canvas strips, 15 feet long and 3 feet wide, are usually employed to identify 
landing sites. These are visible to the pilot at altitudes up to 9,000 feet and indicate 
to the airman the direction for approach. The strips are arranged in the form of 
a T, the approximate outline of the airplane; a long strip is laid crosswise below the 
T to mark the point of contact with the ground, the machine being brought to full 
stop when on the T itself. 























































































114 


Practical Aviation 



Figure 87 —Airplane gliding Figure 88 —The pancake landing 


LANDING 

Making a proper landing is one of the most difficult and most important 
tasks that confront the student aviator. The success of the landing is largely 
dependent upon nosing the machine down at the proper distance from the 
landing field and choosing the proper gliding angle. Thus, if the angle is 1 in 
654 and the machine is at 200 foot elevation the maximum distance allowed 
for the descent would be 200 X 6*4 = 1300 feet from the landing spot selected. 
If a greater distance is allowed, the machine is liable to fall short. A distance 
less than this maximum is preferred, since a spiral may be made to kill extra 
height and a correction of gliding angle made if the angle selected is not the 
best. All airplanes are designed to assume their gliding angle with power and 
thrust cut off. 

OPERATION OF CONTROLS 

When the descent is to be made the engine is throttled down to relieve strains 
on the airplane and insure flexibility of controls. Since the proper gliding angle is 
determined by the speed, the tachometer or the air speed indicator should register 
the determined speed within 5 miles an hour. The machine should be headed directly 
into the wind, the direction of which may be determined by observation of chimney 
smoke or flags below. When within 15 feet of the ground the tail control is gently 
pulled back, elevating the tail until the airplane is in its horizontal position for slow 
flight. This should be accomplished when 5 feet above the ground and the control 
then held; the airplane will thereafter descend without further assistance. The control 
should be held lightly, however, to correct for bumps. 

When about to effect a landing a glance should be directed to the horizon or the 
banking indicator, and the aileron control used to keep the airplane laterally level. 
Swerving as the machine touches the ground is corrected by the rudder or the tail skid. 

BAD LANDINGS 

If, when the airplane is about to land, it assumes the position of flight 
shown in Figure 88 it will bounce when it strikes the ground, the running 
gear breaking on the second impact. Also, if brought out of gHdi ng position 
when too high off the ground it will drop, due to lack of speed, and the same 
break follow. These landings are known as the “pancake.” The remedy is 
to speed up the motor to regain velocity and flying position, then throttle 
down and land. 

The most dangerous landing is caused by failure to pull the airplane from 
gliding to flying position, the running gear striking the ground at a forward 
inclined angle. The motor must be instantly opened wide after the first 
bounce, flying speed being regained before the rebound. 

A bad landing which severely strains landing gear and causes wheels to buckle, 
follows contact with the ground when the rudder is turned, causing a swerve, or 
when the airplane is not level laterally. 







Equipment for Long Flights 


115 


PREPARATIONS FOR CROSS-COUNTRY FLIGHT 

Qualifying tests for Junior Military Aviator prescribe two cross-country 
flights, one of approximately 60 miles and the other 90 miles. When these 
flights are undertaken the student aviator is expected to know all the funda¬ 
mental technique of flying, turning and landing, and have reached the stage 
where the operation of controls is no longer a task but a matter of instruction 
routine, so to speak; in flying cross-country, therefore, he is enabled to give 
a large share of attention to following the course and selecting proper places 
should an emergency landing be required. Prior to the flight a few matters of 
importance require attention. 

EQUIPMENT 

The usual flying clothing is worn, the only caution being to provide for sufficient 
warmth. Leather suit and helmet are worn, supplemented in winter by sweaters and 
mufflers. Hands and feet are most sensitive to cold and should be well protected; 
provision of large boots with woolen socks or stockings will repay the aviator in 
comfort. On a long flight it is well to take two pair of goggles, in case one pair 
should be lost or broken, and a handkerchief to clean them is necessary. An identifi¬ 
cation card and money should be carried for emergencies; the telephone number 
of the airdrome should also be noted and a complete set of tools and covers for 
propeller and cockpit should be carried. 


STANDARD EQUIPMENT—AIRPLANE TOOL CIIEST 


(Cover) 

1 Rule, folding. 

1 Hacksaw frame. 

1 Dividers, pair 6". 


2 Center punches. 

24 Blades, Hacksaw, coarse; 12 
blades, Hacksaw, fine; 1 chisel, 
cold, l /i "; 1 chisel, cold, 34". 

1 Calipers, 6". 

1 Wrench, monkey, 6". 


1 File holder. 

1 Spoke shave, 3". 

1 File cleaner. 

10 Files, assorted, with canvas roll. 
1 Screwdriver, 4". 

1 Palm, sewing; 8 needles, assorted; 
1 ball flax and 1 ball wax. 


1 Wrench, 7". 

3 Reamers, taper, bit stock, 1J4, 
1 5-16, and 154". 

1 Hatchet, half (small). 

1 Snips, tinner’s. 

The machine should be carefully inspected, from tires to instrument board, before 
the start. Wires, controls, engine and gasoline and oil reservoirs are matters to be 
looked into by the aviator, who must not accept the word of mechanicians that every¬ 
thing is ready. The instruments required are a compass, wrist watch, altimeter, 
tachometer, inclinometer and a map board or case. The map case is highly preferable 
as maps pinned to a board often blow off or are torn in long fast flights. 

The map is a most important part of the aviator’s equipment for a cross-country 
flight. It should be placed in a position of easy visibility, such as on the instrument 
board, or, in any event, as nearly as practicable straight ahead in the line of vision. 
The course should be carefully mapped out and notations made, as discussed in suc¬ 
ceeding pages. On a long journey a weather report obtained by telephone from the 
point of destination may save trouble should fogs or storms be prevalent there. 


1 Saw, hand, 26" 

1 Hammer, riveting, 8 oz. 


1 Combination square, bevel and 
level, 12". 


1 Wrench. Stillson, 14". 
1 Screwdriver, 8". 

1 Screwdriver, 7". 

1 Screwdriver, 5". 

1 Nail-puller. 

1 Knife, draw 8". 


1 Bit, expansive, to 3' 
1 Pliers, round nose, 6". 

1 Pliers, snipe nose, 4". 

1 Pliers, adjustable, 8". 

1 Pliers, side-cutting, 8". 

1 Pliers, adjustable, 6". 


(Top) 

1 Hammer, tinsmith’s, 1 pound. 

1 Hammer, claw. 

1 Tape, steel, 100 feet. 

1 Brace, 10". 

1 Iron, soldering, \]/ 2 lbs., 1 iron, 

soldering, jeweler’s. 

(Upper Drawer) 

2 Pliers, auto, combination cutting, 

6 and 8". 

1 Nipper-cut, 7". 

2 Pliers, diagonal, 6". 

1 Pliers, compound, side-cutting, 
8". 


1 Stone, carborundum, 5". 

1 Torch, gasoline, flat. 

1 Set thin open-end wrenches 
with canvas roll. 


(Lower Drawer) 

1 Set drills, Morse, straight shank, 
with canvas roll. 

1 Plane, block, 154". 

1 Drill, hand. 


PHYSICAL FITNESS 

The aviator should have no hesitation in informing his instructor or flight com¬ 
mander of any indisposition; if he does not feel well a cross country flight should 
not be attempted, as the correct functioning of all his faculties will be required. A 
long flight on an empty stomach is bad, as dizziness often results. At least a hot 
drink should be secured, and a good meal if possible. Food in tablet form, chocolate 
or biscuits may be taken along, but should be placed in a position of easy access. 




116 


Practical Aviation 



A military flight in formation; steering by compass in the clouds 









117 


Compass Variation and Deviation 





Figure 89 Compass card Figure 90— J / ertical Figure 91 —Adjusting the compass 

Compass 

USE OF THE COMPASS AND ITS ADJUSTMENT 

The compass is an instrument for indicating the magnetic north by a 
magnetized needle on a pivoted card. While cross-country flight is possible 
with the aid of a map and identifying landmarks, at times when these are 
obscured the compass is a necessity to the aviator. Steering by compass ac¬ 
curately, reference to the map is not required in flight, providing preliminary 
calculations are accurately made as later outlined in this chapter. 

THE COMPASS CARD 

The card is illustrated in Figure 89. Marking in degrees is clockwise, the circle 
beginning at N (north) as zero, and comprising 360 degrees. The card is also 
marked in the old form of the merchant marine; north, east, south and west being 
represented by 90 degrees, bearings being read, for example, 20 J W. of N. An 
aviation compass of the vertical type is illustrated in Figure 90. 

COMPASS ERROR 

VARIATION—The compass indicates the magnetic north from any given place; 
i. e., the compass magnet points to the north magnetic pole, situated on a northern 
Canadian island. This is not the “true” north, and it is therefore necessary on maps 
of the various parts of the earth to make the correction known as variation. This 
is the angle between the true and magnetic meridian at the point mapped. 

DEVIATION—Since the compass needle is magnetic and the airplane contains 
much metal of magnetic attraction an error known as deviation is caused which deflects 
the needle some degrees to the east or west. 

Adjusting the Compass —To correct the deviation error is a task seldom assigned 
to the aviator, but some idea of how it is accomplished will be found of value. (The 
process which we term adjusting, is known in England as “swinging” the compass.) 
The airplane is placed with its fore and aft axis exactly north and south, either by 
aligning it with a tripod “land” compass placed nearby, or by placing the airplane 
on a cement slab provided for the purpose in many flying fields. The airplane is 
trued up, in the latter case, by spirit level and plumb line, as illustrated in Figure 91. 
The compass has what is known as the “lubber’s line,” which is then fitted to the 
fore and aft line of the airplane. The compass reading is then taken, and by inserting 
small field magnets in slots provided for the purpose, the east or west deviation of 
the needle is corrected until it points north with the cement slab. When the best 
correction possible has been made a deviation card is generally made out and placed 
near the compass, for in long flights to a definite objective an error as small as 2 or 3 
degrees will throw out the aviator’s calculations. A specimen of these cards follows: 

For Magnetic Course Steer by Compass For Magnetic Course Steer by Compass 


0 degrees 

357 degrees 

S. 

180 degrees 

183 

degrees 

45 

47 

s. w. 

225 

223 

ii 

90 

90 

w. 

270 

270 

a 

135 

137 

N. W. 

315 

317 

it 


PLACING THE COMPASS 

The proper location of this instrument is an important matter. It should be 
placed in clear view and directly in front of the pilot, preferably in the center fore 
and aft axis of the airplane, as far as possible from moving metal parts such as those 
of the engine. Metal parts such as control levers and rods, if within 2 feet of the com¬ 
pass, should be non-magnetic, and movable equipment such as machine guns, should 
be in normal flying position when the compass is adjusted. After any required change 
in parts is made the compass deviation should be checked and any necessary 
readjustment made. 









































118 


Practical Aviation 



Figure 92 —A typical military map 



maps 




Figure 94—FI eight, distance and 
direction symbols 

































































































































































Meaning of Map Signs and Symbols 


119 


MAP READING 

(Abstracted from Signal Corps Manual, by the same Author.) 

The aviator must know how to read a map before cross-country flights 
can be made. An understanding of the meaning of conventional symbols and 
application of the scale are the main essentials, extensive knowledge not being 
necessary. 

A typical military map is shown in Figure 92. 

DEFINITIONS OF TERMS 

In mapping, many terms are used, a number of which, such as basin, crest, gorge, 
knoll, plateau, and watershed are universally familiar. A few special terms are defined 
here, however, for the simplification of the subject. 

Bearing —The relative position or direction with the north, or true meridian; magnetic bearing, 
the relative position or direction with the magnetic north. 

Contour —A line designating the shape, outline or boundary at a fixed height of a section of 
ground; contours are used to indicate elevations, each contour representing a rise or fall in feet from 
those surrounding it. Illustrated by A, Figure 94. 

Gradient —This indicates a slope expressed as a fraction, a gradient of 1-50 designating a rise of 
1 foot in 50. 

Datum —A fixed level (generally sea level) from which all heights are measured. 

Hachures —A shading method of representing hills, short strokes being drawn directly down the 
slopes. Illustrated by B, Figure 94. 

Meridian —A true north and south line. 


ORIENTING 

The first thing to be determined is: Where is the north? On a map this is usually 
indicated by an arrow placed in one of the corners. Some maps do not have an arrow, 
in which case it is a generally safe assumption that the top of the map is the north. 
When two arrows appear, as in D, Figure 94, one points the true north, the other the 
magnetic north. Usually they are so marked, but if not lettered, the incomplete or 
less elaborate arrow represents the magnetic north. The magnetic north is the north 
of the compass; its deviation from the true north has already been explained. When 
the map has been turned to its proper position, i.e., the magnetic north arrow cor¬ 
responding with the compass, it is said to be oriented. This is the first step for the 
aviator about to lay out a cross-country flight. 


THE SCALE 

Having located his position on the map, the next feature for the aviator to study 
are the distances between points. These are shown by the scale, which appears usually 
on the lower end of the map; for example, two points are measured by ruler on the 
map and the distance is 1 inch; the scale reads: 1" — 1 mi. (as in C, Figure 94), then 
ihe actual distance between these points over the ground will be found to be 1 mile. 
Some maps state: (so many) miles to the inch; the measuring procedure is the same, 
allowance being made for 2 miles to the inch, or whatever the scale states. What is 
known as a representative fraction is sometimes used. On the map, Figure 92, this 


appears as 21120 • If the R.F. is "jqq"~ it means that an inch on the map is equal to 100 


1 

inches on the ground; the fractions are usually large, such as ^3 , which would indi¬ 

cate an inch to a mile, since there are 63,360 inches to a mile. On foreign maps YoOOOO 

is a familiar fraction, and may indicate either inches or millimetres; in all forms the 
principle is the same and the scale is reckoned in the same way, afterwards being 
calculated in inches by the aviator. Another method of showing the scale is illustrated 
on the map, Figure 92, where it is only necessary to copy the scale on a strip of paper 
and apply it directly to the map, reading off the distances between any designated points. 


CONTOURS 

Contours on a map show the elevations, depressions, slope and shape of the ground. 
Hachures, (see B, Figure 94), sometimes used on European maps, show elevations 
only and are of little value. The method of indicating features by contour lines is 
clearly shown in the illustration A, Figure 94. The irregular, curving lines which 
appear on the map represent the outlines of the hill at equally spaced vertical intervals. 
If, for example, by use of a surveying instrument a line of stakes was placed around a 
hill, each one exactly the same height above sea level, a line drawn on the map through 
all the stake positions would be a contour. Study of the diagram A, Figure 94, will 
make it clear how the steepness of hillsides is determined from the map, contour lines 
close together indicating a steep slope, and far apart, a gentler slope. 

On some maps contours are numbered in elevation in feet above the datum plane, generally sea 
level. Thus, at a glance, the elevations are clearly determined. 

The principal conventional signs used by the U. S. Army are given in Figure 93, 
and should be memorized. 








120 


Practical Aviation 




Figure 94—How an airplane must be steered off the direct Figure 95 —Diagram solution of the flight from A to B shown 

course to allow for side wind drift in Figure 94 

























Calculating Drift 


121 


LAYING OFF A COURSE 

DETERMINING THE STEERING DIRECTION 

It is obviously important for the aviator to know the direction to head his 
machine to arrive at a given destination. When flying above clouds, over water, or 
at night, when landmarks are not discernible, he has no means of determining how far 
the wind may be blowing him off his course. Calculations are therefore made in 
advance by the following method: 

DATA REQUIRED: 

Flying speed of his airplane. 

Compass bearing of his course from point of departure to destination. 

Direction and speed of the wind. 

The map of the country over which he is to fly will give him the compass bear¬ 
ings; the points joined by a line (see Figure 94) determine the direction and its angle 
to the north of the compass bearing. 

Direction and speed of the wind can be found from the weather vane and anemo¬ 
meter of the airdrome. The anemometer is a device with four arms carrying cups on 
the end of each, turning about on a vertical axis at a speed varying with the wind 
velocity. When the wind velocity at the ground has been determined, the aviator must 
decide upon the height at which the flight is to be made, for as height increases the 
velocity and direction of the wind changes. The table below will be found useful in 
estimating the proper allowance: 


Wind Velocity and Direction Changes With Altitude 
(Based on Wind Velocity of 25 miles per hour ) 


Height in feet. 

At the earth’s surface 

500' 

1000' 

2000' 

3000' 

4000' 

5000' 

Velocity change in per cent.... 

100% 

135% 

172% 

188% 

196% 

200% 

200% 

Clockwise deviation in degrees.. 

0 

5° 

10° 

16° 

19° 

20° 

21° 


Example: Assume that the anemometer shows a wind velocity of 25 miles per hour at the ground, 
and the weather vane indicates the direction of the wind 89° west of north. The aviator plans to fly his 
course at a height of 3000 feet. From the table he learns that the wind velocity at this altitude is 196%, 
greater than at the ground; then, 25 X 1.96 = 48 miles, per hour. Likewise, from the table, it is seen 
that the wind direction at this altitude shows a clockwise deviation of 19°, so at 3000 feet the direction 
of the wind will be 89° —19° = 70° west of north. 

A DIAGRAM TO DETERMINE THE WIND FACTOR 

With the data in hand the aviator can lay out a simple diagram for his course. 
Assume that his orders call for a flight from Fort de \ illeneuve to Bougy (see A-B, 
Figure 94). The route, according to the map, is 30° east of north. The speed of the 
aviator’s airplane is 80 miles per hour. The wind, as already determined, has a velocity 
of 48 m.p.h. in a direction of 70° west of north at 3000 feet, at which height the flight 
is to be made. 

Either on the map or on a separate sheet of paper, the starting point is designated 
A (see Figure 95). A line is then drawn with the proper compass bearing to the 
destination B. From point A a line is drawn parallel to the direction of the wind, blow¬ 
ing 70 degrees west of north. On this line the velocity of the wind is measured off, the 
aviator establishing a scale, say 1 inch = 10 miles, or any other convenient scale. Assume 
that the scale 1 inch = 10 miles is the one selected; then 48 m.p.h. would be measured, 
4.8 inches to point C. With a pair of dividers opened to represent the speed of the 
airplane by the same scale (in this case, 80 m.p.h. = 8.0 inches) an arc is described with 
C as the center. Where it cuts the line A-B (see D, Figure 95) a line is drawn from 
D to C; this line gives the proper direction to steer the airplane to neutralize the drift 
of the airplane in one hour’s flight from A to B in the cross wind. The steering is by 
compass bearing to the fore and aft axis of the machine. 

Measurement of the line A-D, applied to the scale will give the actual velocity in miles 
per hour of the flight. In the example it is seen to be 85 m.p.h., that is, the cross wind 
increases the airplane’s speed 5 miles per hour. 

The student should reconstruct the diagram for the return flight. That it will not 
do to steer in exactly the opposite direction will then be made clear. In all cross¬ 
country flights a separate diagram for the return is required, unless, of course, the wind 
happens to be exactly parallel to the course. 






























122 


Practical Aviation 


RADIUS OF ACTION 

To determine the distance outward the airplane can go and have sufficient gasoline 
to return, requires a simple calculation. 

The aviator knows his gasoline capacity; i.e., how many hours of flight can be 
obtained before the tank is empty. With this and the other data he can figure his 
radius of action in miles. 

Example: Assume that the flight is to be made straight into a head wind of 30 miles per hour, 
the speed of his airplane is 80 m.p.h., and its gasoline capacity 4)4 flight hours. (For climbing and as 
a general margin )4 hour gasoline consumption is deducted, leaving 4 flight hours). 

On the outward trip his speed is 80 — 30 = 50 m.p.h. 

On the return trip his speed is 80 + 30=110 m.p.h. 

The ratio for both trips is, then, as 50 is to 110, or 5 is to 11. The time required for the outward 
trip is thus 11/16 of 4 hours, and the return trip the remaining 5/16 of 4 hours; or, outward = 2)4 hrs.; 
return =1)4 hrs. Since his outward bound speed is 50 m.p.h., then 50X2)4 —137)4 miles radius. Return 
speed being 110 m.p.h., then 110X114 — 137)4 miles. This, then, is the radius of action. 

A wind blowing directly along the course is a rare occurrence, however. A diagram 
similar to Figure 95 must therefore usually be made, both for the outward and return 
trips. The calculation for radius of action is then carried on as above, or by the 
simple formula: 


b X c 

Radius of Action = aX- 

b + c 


Where 

a = gasoline hours, 
b = outward speed, 
c =return speed. 


SOME FLIGHT CONSIDERATIONS 
PROPER PREPARATION 

Care must be observed by the aviator that his preliminary preparations 
are properly made. This refers particularly to a study of the course from the 
map. 

Ordinarily the country over which he is to make the flight will be on one 
sheet with features and landmarks clearly indicated. Should the use of two 
sheets be necessary these should be pasted together before starting and cut to 
fit the map roll. In war flights foreign maps with the scale in fractions are 
often the only ones available; the aviator should immediately construct the 
corresponding scale at so many miles to the inch, which will facilitate rapid 
calculation. Distances from the starting point should also be marked at ten 
mile intervals or by distinctive objects to be passed. High hills should be 
marked as bad for landing. 

HEIGHT 

Where there are no high hills or mountains in friendly territory the flight is best 
made at heights from 1,500 to 3,000 feet. An altitude of 1,500 feet should be attained 
by an initial circling climb before the aviator sets off on his course. Speed and steadi¬ 
ness of wind increases with height, and landing or righting in case of mishap is better 
accomplished with a good margin; but above 2,000 feet contour of the country is not 
readily distinguished, so if the flight is to be at a higher altitude the poor landing 
places should be clearly marked on the map. It is well for beginners to keep the 
ground in view throughout the flight, flying under or around any clouds. 

CLOUDS, FOG AND STORMS 

Pupils are cautioned to avoid heavy cloud banks and not to rise above clouds 
when near the seacoast, for a wind off shore may carry the airplane out to sea with¬ 
out the pilot’s knowledge. When navigation above a cloud bank is necessary, the 
cloud formations may be used as a basis for keeping the airplane horizontally" level, 
for cloud formations are ordinarily sufficiently level for this purpose. Fog should be 
avoided; in fact, when a heavy mist is encountered a landing should be made as soon 
as possible. River valleys should be avoided, for they very often hold a ground fog up 
to a height of 700 feet. At times when the flight must be continued through clouds 
or fog, the instruments should be carefully watched and the stick control and rudder 
kept in central position as much as possible. Heavy rain, sleet and hail chip the pro¬ 
peller slightly and when encountered a landing should be made at the earliest favorable 
opportunity. A whistling sound indicates that the propeller has been chipped 







123 


Remarks on Cross-Country Flight 


AIR DISTURBANCES 

Initial cross-country flights by the student are usually made under favorable 
weather conditions, ordinarily in the early morning or late evening, when the atmos¬ 
phere is calmest. Bumps caused by heat, as explained in a later chapter on meteor¬ 
ology, manifest themselves early in the day as close to the ground as 100 feet; their 
influence is gradually extended upward as the morning progresses until they are per¬ 
ceptible at noon at altitudes up to 3,000 feet. Clouds and inland waters generally 
predict bumps, while over the sea the air is ordinarily smooth, although of high 
velocity. Landings in strong, bumpy winds are best made with additional speed, 
caution being exercised when nearing the ground in sheltered spots as wind eddies 
may cause a sudden roll or a drop of 10 feet or so. 

LOST BEARINGS 

Should something happen to the compass and the aviator be unable to get his 
bearings, his wrist watch will be of assistance in locating the points of the compass. 
With the hour hand pointed to the sun, the point midway between the angle it makes 
with the numeral 12, points to the south. Thus, at 8 o’clock in the morning, with the 
hour hand pointed at the sun, the point midway in the angle formed by 8 and 12, i.e. 
10 on the watch dial, will point to the south. 

LANDMARKS 

The principal landmarks of a map should be firmly fixed in the aviator’s mind prior 
to the flight, memorized if possible. Experience has shown that the following features 
are the most useful: 

Towns —These are the best guides and should be marked with a circle or under¬ 
lined on the map. A village is sometimes difficult of identification; location of its 
church and its reference to the roads will aid in placing it. If flying below 2,000 feet 
attitude the aviator should not pass directly over the town as the heat from factory 
chimneys causes marked air disturbance. 

Railways —Railroad tracks are of great assistance. Tunnels, bridges and cuts are 
marked on the map and aid in locating the line to be followed should the aviator mis¬ 
take a branch line or siding for the main route. It should be remembered that the 
track disappears when it passes through a tunnel. 

Water —Water courses and lakes are usually clearly defined and may be seen at 
some distance. Allowances should be made, however, for possible flooding of streams 
after heavy rains which may change their appearance as recorded on the map. The 
bearing of a river with reference to the course should be noted; following its windings 
may involve loss of time. 

Roads —From a height all roads look very much alike and are therefore not very 
good guides. Main roads can occasionally be identified by the paving and the amount 
of traffic, and are useful because they lead into towns. Telegraph lines may be expected 
along them, which makes landing nearby dangerous. 

Woods —Small forests serve as excellent guides. 

Hills —From altitudes of 2,000 feet and over, hills are flattened out in appearance 
and valleys are not clearly discernible. 

General Characteristics —’The physical features of the country are very helpful to the aviator if his 
preliminary study of the map fixes in his mind their relationship to each other. How railways and streams 
join or intersect, how they enter and leave towns, and their relation to wooded areas, supply useful 
information. Dividing the course into four progressive parts also aids, if the general nature of each 
sector is noted for its chief distinguishing characteristics, whether water, woods, farm lands, towns or 
villages. 

FORCED LANDINGS 

Engine failure is the main cause of forced landings. As soon as it is known that 
the failure is complete, the engine should be switched off and the gasoline pipe closed 
to lessen the danger of fire. The airplane is then turned into the wind and if the 
ground directly beneath makes landing impossible the descent can be made in a long 
glide. While selection of landing ground is not practical from a recognition stand¬ 
point at altitudes greater than 1,000 feet, entirely unfavorable areas such as water, 
marshes or forests may be avoided by long glides. The radius of the forced landing is 
about five times the height at which the airplane is flying. An aviator forced to land 
from a height of 2,000 feet, therefore has about 10 square miles of land to choose from. 
At a height of 5,000 feet he has selection in an area of about 70 miles. 

When a forced landing has been made the aviator’s first thought should be for his machine and the 
immediate possibility of resuming flight. Examination of the engine is the first step; it should then be 
determined how much, if any, damage has been done to the airplane structure. A telephone call to his 
headquarters should then be made and a report given of his location and diagnosis of the trouble. If the 
damage requires staying where he is for the night, then the airplane should be moved to some spot 
sheltered from the wind and made secure. 









124 


Practical Aviation 


TIME CHECKING 

It is difficult to estimate time while flying, yet checking by the watch the time 
when successive objects are passed is an important detail often overlooked. The 
tendency invariably is to expect the next landmark long before it is due and confusion 
will arise in the aviator’s mind unless time elapses are carefully checked. Knowledge 
of elapsed time is also valuable in steering a compass course over the clouds. 


SELECTING LANDINGS 

Choosing a suitable field to land in is by no means an easy task for the novice. A 
few primary rules governing selection will be useful. 

It is better to pick out a group of Helds as the glide may take the inexperienced aviator 
beyond or short of the mark. 

Stubble Helds, brown in color from a height, are generally smooth and, excepting 
sandy beaches, make the best landing ground. 

Grass Helds, green in appearance, often can be identified by cattle grazing. Mounds may 
be looked for in grass land, so they are therefore second choice. 

Cultivated land is ordinarily fairly level, but landings made therein are successful only 
when pancaked. A ploughed field is black in appearance, vegetable and corn fields 
have a hue considerably darker than the green of grass lands. 

A field near a town is the best choice, as its proximity to the source of supplies is a 
great convenience. The landing field selected, however, is preferably to windward of 
the town, so it will not be necessary to rise over the buildings when re-starting. 

Telegraph wires usually border main roads and railways; these wires cannot be seen 
until the aviator is close upon them, so nearby landing places are undesirable. 

When snow is on the ground the selection of a good landing place is practically impos¬ 
sible; the frozen ground, however, makes its selection of less importance. 

Light variations are important. Flying into the rays of the sun, a slight haze appears 
which distorts objects. In the late evening, too, the light may be good at the flying 
altitude, but when descent is made the ground appears much darker. Before landing, 
therefore, a wide circle should be made until the eyes are used to the relative dulness. 


PEGGING DOWN 

The airplane should be placed head into the wind and the tail lifted up and sup¬ 
ported at a height which will place the airplane’s wings edgewise to the wind. The 
controls should be locked and the wings and fuselage near the tail pegged down, some 
slack being left in the rope. The propeller, engine and cockpit should then be covered. 
If a strong wind is blowing, trenches should be dug for the wheels to a depth of about 
Yx their diameter. 

RE-STARTING 

A minor trouble which does not require calling a repair crew may leave the 
aviator without assistance for starting, although spectators willing to hold back the 
airplane are generally more numerous than too few. Stones or fence poles will serve 
as chocks under the wheels if assistance is not at hand. Any mud which may be gath¬ 
ered on the wheels should be cleaned off as it will be drawn to the propeller by cen¬ 
trifugal force and chip or break it. Before starting, the ground over which the machine 
is to taxi should be walked over carefully and any serious obstacles removed. The 
possibilities of dead wind in the lee of buildings should be estimated and allowance 
made to get clear of these areas as the airplane rises. Small obstacles, such as hedges, 
may be cleared if good taxying speed is acquired and the control stick pulled back 
suddenly. Getting rid of extra weight will also aid the machine to take the air quicker, 
should there be doubt of getting out of the field. 




Practical Aviation 


125 


REVIEW QUIZ 

Instruction in Flying 
First Flights and Cross-Country Flights 

1 . Give in simplified form the results of manipulating the stick control 
to its four positions and the effect of ruddering to right and left. 

2 . Why should the airplane be headed into the wind at the start? 

3. What is the minimum taxying distance a beginner should allow before 

rising from the ground? 

4. State a safe altitude margin for turns, the proper turning speed for 

the novice, and give the cause of side-slips while turning. 

5. In an S-turn how does the landing spot selected serve as a guide? 

6. Give three elementary rules of the air which determine right of way. 

7. Explain how landing sites are identified and on what portion of the 

mark should the airplane be brought to a full stop. 

8. By an example, state the rule for gauging the distance allowed for 

descent to the landing field. 

9. Name the essential equipment and the necessary inspection required 

of an aviator prior to cross-country flight. 

10. Define compass variation and deviation and a method of adjusting 

the compass. 

11. Lay off a course by diagram for a flight of 100 miles in a direction of 

12 degrees east of north, in an airplane with speed of 75 m.p.h. 
and a wind blowing 48 degrees east of north with a ground 
velocity of 25 m.p.h.; the flight to be made at 2,000 feet altitude; 
determine by the diagram the proper steering direction to allow 
for wind drift and give the resultant compass bearing. 

12. Given the following data, determine the radius of action of the air¬ 

plane: Head wind blowing 41 m.p.h.; airplane’s speed, 70 m.p.h.; 
gasoline capacity, 3 % flight hours. 

13. In what way are cloud banks useful to the aviator flying above them? 

14. Explain how a wrist watch is useful in determining direction should 

the compass be out of commission. 

15. How are towns, railways and water courses useful as landmarks? 

16. Why are hills and roads poor guides? 

17. Give the reason why checking the time when successive objects are 

passed is important. 

18. What is the difference between a map contour and a gradient? 

19. Explain how distances on a map are determined by the scale and 

describe four ways of marking the scale. 

20. From memory, sketch 15 conventional map signs denoting various 

^ypgs of soil, communications and enclosures. 





126 


Practical Aviation 


CHAPTER ANALYSIS 

Advanced Flying 
Aerobatics and Night Flights 

ADVANCED FLYING: 

(a) Spiral. 

(b) Nose Dive. 

(c) Spinning Nose Dive. 


AEROBATICS: 


(a) 

Loop the Loop. 

(b) 

Flying Upside Down. 

(c) 

Vertical Bank. 

(d) 

Zooming. 

(e) 

Roll Over. 

(0 

The Stagger. 

(g) 

Spiral Loop. 

(h) 

Immelman Turn. 

(i) 

Flat Turn. 

(j) 

General Considerations. 

NIGHT 

FLYING: 

(a) 

Equipment. 

(b) 

Preliminary Instruction. 

(c) 

Taking-Off and Flying. 

(d) 

Landing at Night. 

(e) 

Lighting the Field. 




CHAPTER XII 


Advanced Flying 
Aerobatics and Night Flights 

The course of training which leads to a rating as Military Aviator is 
known as advanced flying. It consists generally of effecting landings among 
obstacles and difficult turns, high altitude flights and long cross-country 
flights; in fact, in acquiring great skill in handling the airplane. Beyond this 
training lies the acrobacy of the air, termed aerobatics, stunt flying which at 
first appears foolhardy but has an exceptional value in war where fast ma¬ 
chines are engaged in combat. 

Ascents to 10,000 feet or more may be classed as advanced flying, although 
these climbs present few difficulties and little danger. On the assumption 
that all aviators are plentifully supplied with courage, climbing for the first 
time to high altitudes is largely a matter of patience. 

A pertinent suggestion to novices in lofty climbing is not to imagine the 
engine is stalling as height increases; the rarefied atmosphere will require 
less steep climb in higher altitudes, but that is a matter for adjustment, the 
best angle for the particular machine being determined by the aviator’s obser¬ 
vation of altimeter and watch, and their relation to the airplane’s flight 
efficiency. 

Descent from the first 10,000-foot flight is best made slowly, so the aviator 
may become accustomed to variations in air pressure. Any discomfort in 
breathing can usually be relieved by swallowing at frequent intervals. It is 
advisable, too, when the airplane has come within 1,000 feet of the ground, to 
circle once over the flying field for the purpose of refreshing the memory on 
the appearance of the ground at that height. 

Application of the principles of aerobatics explained in this chapter 
should be preceded in flight by some hours’ practice in climbing turns and 
stalling turns at altitudes of 2,000 to 3,000 feet. Getting close upon other 
airplanes without being seen is also valuable maneuvering practice. Not 
every pilot is successful in learning aerobatics; comparatively few, in fact, 
are designated by the instructors to master these air evolutions; but the heady 
man who is physically fit takes to this form of flying readily and is fairly 
certain to come out with a whole skin if these two primary rules are rigidly 
observed: 

1 . Always leave a wide altitude margin between the airplane and the 
ground. 

2 . Do not effect too sudden changes of direction; straighten out grad¬ 
ually after diving. 


127 


128 


Practical Aviation 



(C) Int. Film Svce. 

Figure 96 —An American air squadron dying in formation over the City of New York 
to demonstrate the absolute control of the pilots in bumpy air 






Spirals and Nose Dives 


129 



Figure 97 —Descending 
spiral 


Figure 98—A lose Dive Figure 99 —Spinning 

nose dive 


SPIRAL 

Descending spirals, illustrated in Figure 97, are made by a continuous series of 
banked turns in the same direction with nose slightly down. The aileron control and 
ruddering are governed by the steepness of the descent desired, the controls ordi¬ 
narily being held steady until the descent is accomplished to the designated point. 
The aviator constantly looks inward and downward toward the center of the circles 
he describes, an occasional glance at the banking indicator serving to inform him of the 
accuracy of his turns. Care should be exercised that the nosing down does not become 
too steep, or a spinning nose dive will result; too steep and rapid descent is corrected 
by slightly pulling back the stick control. 

iNOSE DIVE 

The nose dive is accomplished by shutting off the engine and pushing forward the 
control stick suddenly. The dive may be made with engine running, but this subjects 
the airplane to severe strains and should be avoided. First dives should not be as 
steep as that shown in P'igure 98, and the novice should learn the trick far above the 
ground. At not less than 1,000 feet altitude the airplane should be straightened out; 
this is accomplished by a firm but gradual backward pull on the control stick. When 
the air speed indicator registers low flying speed the control should be centered and 
the engine switched on. 

SPINNING NOSE DIVE 

From the spiral it is very easy to go into a spinning nose dive, illustrated in Figure 
99. While it is a recognized maneuver of air tactics, the spinning nose dive is generally 
the result of slowing down in the spiral, which then becomes too steep, the tail planes 
acting, so to speak, as a vertical rudder, and the rudder functioning as an elevator. 
The revolutions and fall of the machine are very fast; the aviator should avoid looking 
at the ground while in the spin. 

To get out of a nose spin, both feet should be evenly pressed against the foot bar 
until it is held straightened; this evens up the rudder and stops the spinning. The 
control stick is then brought to center and back; then pushed forward. A steady pull 
back, and the airplane levels out. The engine throttle is then opened and the flight 
parallel to the ground continued. 


















130 


Practical Aviation 



LOOP THE LOOP 

Looping the loop is a comparatively simple and effective air evolution. 
A height greater than 3,000 feet should be selected and the descent begun at 
a more gradual angle than employed in the nose dive. When, with the aid 
of the motor, a speed of 75 miles per hour, or better, has been attained, a firm 
backward pull on the control stick causes the airplane to rise and turn over. 
The backward pull should begin at point 1, Figure 100, and the stick be all 
the way back at point 2. When the airplane is upside down and the ground 
visible below, the motor may be cut off (point 3, Figure 100), in which case 
the airplane will describe the smaller loop along course A. The stick is held 
back steady until point 4 is reached, when it is steadily moved forward to 
center, the motor being switched on at point 5. The loop can be made with 
the engine on, but the recovery will not be as quick, the airplane following 
the course B. 

Special cautions—Control movements in looping should be steady and 
firm; jerkiness may produce dangerous stresses and lead to possible collapse. 

The aviator’s safety belt should be securely adjusted and seat cushions 
removed. 

Looping is best done against the wind. 

FLYING UPSIDE DOWN 

This maneuver is executed the same as looping up to point 6, Figure 101. 
Here the engine may or may not be throttled down. If the engine speed is 
reduced the steeper course D must be taken, as there is danger of stalling at 
a lesser angle. With the engine on full, the stick control is pushed forward 
to center, at point 6, the airplane then flying upside down in the approximate 
course C. 




Vertical Bank, Zooming, Roll Over and Stagger 


131 



Figure 102 ( Upper)—Vertical bank Figure 104— The roll over, also known as the barrel 
Figure 103 ( Lozver)—Zooming 

VERTICAL BANK 


Banking at angles greater than 45 degrees is known as vertical banking. No par¬ 
ticular difficulties are encountered in these exaggerated turns, but the aviator must 
become accustomed to the reverse order of control functions while in this position. 
See Figure 102. 

The vertical bank is accomplished by pushing both aileron and rudder controls far 
over in the desired direction. Once the airplane is on its side, the tail elevating planes 
act as a rudder and the rudder’s function is that of the elevator. 

The next step after banking is to level the airplane horizontally with the horizon. 
Pushing the rudder bar with the foot which is uppermost will raise the nose, and rud¬ 
dering from the bottom will lower the nose. To turn the airplane while on its side the 
control stick is eased back slightly in the direction opposite its position for the original 
banking. 

Coming out of the vertical bank, the stick control is pushed full over to the opposite 
side, and as the airplane reaches a position nearly horizontal, opposite ruddering is 
given to the degree necessary, the stick control then being centered a trifle forward. 

The aviator should remember that the rudder is not to be thrown over until the 
machine is near the horizontal, for its action has changed; it is acting as an elevator 
while the airplane is on its side, and raising the nose may result in a stall. 

ZOOMING 

This consists of a sudden upward rise or jump while flying at high speed. It is 
illustrated in Figure 103. The upward rise is obtained by pulling the stick control back 
suddenly. The machine’s climb ends with the stalling point, when the control stick 
must be pushed forward again. The stalling point is best made known to the aviator 
by the sloppy feeling of the controls; the air speed indicator may also be consulted, 
but it is not so reliable by reason of the lag. Caution must be exercised in zooming 
that the control is pushed forward and speed regained before the airplane stalls, or a 
dangerous tail spin may result. 

ROLL OVER 

A very effective and comparatively easy evolution is rolling, also known as the 
barrel, or roll over. The airplane at high speed is made to trace an air course like a 
screw thread, as illustrated in Figure 104. 

The roll over may be begun at a speed of about 95 miles per hour, the control 
stick being thrown away over to the left (or right) throwing the left aileron up and 
the opposite aileron down; the feet are kept still on the rudder bar. 

Coming out of the roll is accomplished by bringing the control stick back to center 
just as the airplane levels out at the top of a turn. 

THE STAGGER 

A veritable see-saw may be made out of the roll over by giving the stick control 
a circular motion and alternately pushing right and left on the rudder bar in synchron¬ 
ism as the stick successively comes round right and left. 
























132 


Practical Aviation 



Figure 105 —The spiral loop 


Figure 106 —The Immelman turn 


SPIRAL LOOP 

This is a difficult evolution, but it has the special advantage of bringing the aviator 
back to approximately the same position from which he started and headed in the same 
direction. The course of the airplane is shown in Figure 105. 

The beginning is the same as for looping; when the machine, upside down, reaches 
the top of its loop, however, the motor is cut out and the control stick pushed sharply 
forward, the rudder being kicked sharply left (or right). The airplane begins to fall 
on its back and spin slowly around; at the half-turn, the rudder is centered and the 
stick pulled back until the machine straightens out. The engine is then switched on and 
the level flight continued. 

IMMELMAN TURN 

The course of this famous German evolution is shown in Figure 106. It consists 
of turning the airplane over sideways as it begins to zoom, and righting it so it comes 
down in the opposite direction. It can be done with engine on or off. 

The evolution is begun just like the loop, the control stick being pulled back two- 
thirds of the way for the steep ascent. When the machine is at the vertical position; 
the foot bar is pushed over left (or right) throwing the rudder and causing the airplane 
to describe an inverted U to the left. As it noses down the control stick is pulled 
back the remaining one-third and the elevating planes straighten out the airplane 
parallel to the ground. 

FLAT TURN 

A useful maneuver in air fighting is the flat turn, which enables the aviator to make 
a quick sweep to the side. This is accomplished by cutting off the engine for an instant, 
kicking the rudder bar full over, then centering it. The side sweep is through an arc 
of about 90 degrees; most of the flying speed is lost in the turn. Centering the rudder 
quickly after throwing the bar over prevents the airplane from entering into a spin. 


GENERAL CONSIDERATIONS 

Height—The aviator who engages in aerobatics cannot be cautioned too strongly 
about allowing a good altitude margin. A miscalculation of speed or distance, or 
engine failure, has many times resulted in a fatality when the machine was too close 
to the earth. 

Bumps—In aerobatics it is a common experience for the aviator to encounter 
bumps caused by the air disturbances created by his own machine; these are not serious 
and should give no cause for alarm when encountered. 

Lost Control—A general rule for safety when the airplane gets out of control is 
to throttle down or cut off the engine. If at a good altitude the nose dive should then 
be attempted. An unexpected spin should not cause confusion, because if the rudder 
is held firmly in the center position, with sufficient altitude the airplane will right itself. 








Night Flying 


133 



From painting by Lieut. Farre 

lights and the method of lighting the landing held 
Bombing airplanes returning at night from an air raid, illustrating the use of search- 

NIGHT FLYING 

Nearly all bombing raids and air offensives are conducted at night; flying 
after dark is not particularly dangerous under instruction conditions, but con¬ 
siderable skill is required for a night raid over hostile territory. 

EQUIPMENT 

The airplanes used are generally those of marked stability, thus relieving the pilot 
of the mental strain of control; for this reason, also, aviators ordinarily make a night 
flight in machines with which they have become thoroughly familiar in daylight. The 
figures on instruments are treated with luminous paint and two shaded electric lights 
are ordinarily provided to illuminate the dashboard. Another electric light is usually 
placed on the floor of the cockpit. Flares for use in case of forced landing are 
included; these are of the parachute type and include in the equipment an electric 
launching tube. Navigation lights are placed on the wing tips, red on the left, green 
on the right, and a searchlight is generally included to light up the ground when 
landing. Electric current is principally used for these searchlights, a yellow metallic 
mirror reflector throwing a ray which best penetrates mist. The flares have the 
advantage of illuminating a mile or so area for about four minutes, whereas the 
searchlight rays are confined to a small radius; both are usually carried, however. An¬ 
other lighting scheme provides a row of electric lights with reflectors, placed under 
the leading edge of the lower wings. The propeller and bright metal parts are 
painted black so as not to dazzle the aviator’s eyes. 

PRELIMINARY INSTRUCTION 

Practice for night flying broadly includes a daylight rehearsal of exactly how 
the airplane will fly at night. Flying by the instruments alone, without guiding by 
the horizon, should be accomplished; slow glides should be practiced; small side¬ 
slips and quick recoveries should be effected; slow landings and turning with the 
instruments as the sole guide perfected, and the pilot should become accustomed to 
the sound or “sing” of wires at different speeds and varying conditions. 

An aviator’s fitness for night flying is generally gauged by his success in making 




134 


Practical Aviation 


a half-dozen or more solo landings in the darkness; night instruction by dual control 
is seldom given. 

An essential portion of his knowledge is thorough familiarity with the country 
over which he is to fly at night and full acquaintance with the airdrome in which 
he is to land. 

TAKING-OFF AND FLYING 

As the airplane is wheeled into position the aviator carefully notes the lighting 
and layout of the landing ground in the airdrome. The landing is usually indicated 
by a chain of lights in the form of an L, those at the lower end marking the point 
before which a full stop must be effected. The lighting is arranged so the wind 
blows up the long arm of the L, and the machine is faced into the wind for the 
start at the end, or top, of the letter. The number and spacing of the lights is fixed 
by the commanding officer; these should be counted by the pilot and an estimate 
made of the distance allowed for taking-off; obstacles should be noted, for the landing 
on the return is to be made on the same ground. Taking-off at night has one impor¬ 
tant difference from daylight flying; at night the airplane is allowed, so to speak, to 
rise from the ground itself, the instant when it becomes difficult to hold the machine 
down being the proper time for the take-off. 

The rigging for night flying is also preferably changed, so that with the control 
stick neutral the airplane is in a position for slight climb; this adjustment assures 
medium and uniform speed, which is further provided for by adjusting the engine 
throttle so level flight is obtained when it is half open. The take-off is, as already 
explained, made into the wind. 

Night pupils should remain within gliding distance of the airdrome and avoid 
clouds which obscure the ground lighting. Flights made on moonlight nights permit 
the aviator to see his landing field plainly, but it must be remembered that the airplane 
is quickly lost to the view of those on the ground. Railways cannot be identified 
easily, even under perfect conditions, but the white smoke from a train on clear 
moonlit nights and villages and towns are easily discerned, and roads recognized at 
7,000 feet. On moonless nights only lights can be seen from 5,000 feet; rivers, rail¬ 
ways and roads are not distinguishable, but the airdrome flares are easily recognized. 
If other pupils are in the air, the red and green navigation lights are lit at 2,000 feet. 

LANDING AT NIGHT 

The straight glide is the only type of landing to be attempted by the student 
aviator; the glide should begin at least a mile away with the engine turning over 
slowly; when within less than fifty feet of the ground the engine should be switched off 
and the airplane allowed to come down of itself; that is, the nose should not be put 
down. 

Signals for landing are arranged beforehand. By them the aviator recognizes 
his own airdrome, for when over his field and ready to descend he fires the prescribed 
colored light, which is answered from the ground by a light of the color prearranged. 
He then gives the landing signal and the flares are lit for his descent. 

The searchlight, if the airplane is equipped with one, is sometimes switched on 
at about 1,500 feet and the ground searched for the landing field. A pilot flying alone 
will find its manipulation difficult, so at a low altitude it is switched off and a flare 
dropped over the field. If an observer is carried the searchlight is left to his hands. 

LIGHTING THE FIELD 

Proper lighting of a landing field is a matter of extreme importance. There are 
various types and lighting arrangements, but usually gasoline flares or flame arc 
lamps are used, laid out in L-form and aided by searchlights which point into the 
wind, or away from the eyes of the aviator who is landing. When the searchlights 
are used they serve to light up the strip of ground which serves as a runway for 
the airplane. 

Twin, parallel and triangular light arrangements have been proposed and used, 
as well as concentric light circles. The arrangement most in favor is the L, however, 
which is laid out this way: .. ... 

§ * * * * sj: 

Land here ->- - ■<- Wind 

S \ 

In the above diagram S. S. are the searchlights, and the asterisks the flares, 
placed a fixed distance apart and in the number specified by the commanding officer! 
The short arm, or bottom, of the L, designates the point where the airplane must be 
brought to a full stop. Should the airplane not reach the ground before half the 
length of the long arm has been traversed, the aviator should not attempt to land, 
but should switch on his engine and rise for another circuit. 






Practical Aviation 


135 


REVIEW QUIZ 

Advanced Flying 
Aerobatics and Night Flights 

1. Why is it advisable to make a slow descent the first time a height of 

10,000 feet is attained? 

2 . Give two primary rules to be observed when learning aerobatics. 

3. State the direction for an aviator to look while making a descending 

spiral. 

4. How should the control stick be handled in straightening out of a 

nose dive? 

5. Give the reason why a nose dive sometimes becomes a spinning nose 

dive and explain the action of the control surfaces while in the 
latter. 

6 . What are the control operations required to bring an airplane out 

of a nose spin? 

7. In looping the loop, what is the effect on the descending flight path 

if the motor is cut off when the airplane is upside down? 

\ 

8 . What special manner of handling controls is required when looping? 

Give the reason. 

9. Explain how the vertical bank is accomplished and how the action 

of controls is changed. 

10 . How is the airplane leveled with the horizon when in a vertical bank? 

11 . Describe the evolution known as zooming and state the indications 

which announce the end of the climb. 

12 . What action of controls starts the airplane on the barrel, or roll over, 

and how is the machine brought out of the evolution? 

13. Explain the action of the controls which cause the airplane to stagger 

or see-saw. 

14. Describe the successive movements of a spiral loop and the manipu¬ 

lation of the controls. 

15. How does the spiral loop differ from the Immelman turn? 

16. Describe the Immelman turn and how the controls are handled. 

17. What control manipulations are required to make a flat turn? 

18. Give a general rule for safety when an airplane gets out of control. 

19. What details should be mentally noted by the aviator about to begin 

a night flight? 

20 . State in detail the nature of the glide and landing a student should 

make at night and the relation of the field lighting to his landing. 






136 


Practical Aviation 


CHAPTER ANALYSIS 

Meteorology for the Airman 

CHARACTERISTICS OF THE AIR: 

(a) Composition of the Atmosphere. 

(b) Atmospheric Pressure. 

(c) Measure of Pressure. 

(d) Pressure Areas. 

(e) Cyclone Area. 

(f) Anti-cyclone Area. 

(g) Secondary Depressions. 

(h) The Wedge. 

(i) Line Squalls. 

(j) Beaufort Scale. 

WIND CONDITIONS WHICH AFFECT AVIATION: 


(a) 

Wind Distribution. 

(b) 

Aerial 

Fountain. 

(c) 

Aerial 

Cataract. 

(d) 

Aerial 

Cascade. 

(e) 

Aerial 

Breakers. 

(0 

Vertical Wind Eddies. 

(g) 

Wind Layers. 

(h) 

Wind 

Billows. 

(0 

Wind 

Gusts and Eddies. 

(j) 

Aerial 

Torrents. 


CLOUDS AND THEIR SIGNIFICANCE: 

(a) Classification of Clouds. 

(b) General Observation. 




CHAPTER XIII 


Meteorology for the Airman 

In many ways the air is comparable to the sea; in fact, in a large portion 
of the study of the basic principles of aerodynamics the action of the sea is 
used as an analogy. The professional pilot of water craft who lacks knowl¬ 
edge of the ocean is unheard of; and so must it be with the military aviator's 
knowledge of the air. Successful flying over long periods is largely due to an 
aviator’s understanding of the air and its vagaries; in fact, where this 
knowledge does not exist, continued success is entirely a matter of luck. 
Some grasp of the elementary principles of meteorology is therefore essential. 
It may be gained by experience, but this method has more than once led to 
fatal misconceptions. Theoretical instruction, through which ability is 
acquired to apply the scientific laws of weather forecasting, is a safeguard 
well worth the time spent in acquiring it. 

Flying over hostile territory in war time requires the aviator to ascend 
under all types of weather conditions. By thorough acquaintance with 
meteorological factors which bear on aviation, or aerography, as it is aca¬ 
demically called, the pilot may know at a glance what the behavior of his 
machine is likely to be, and will not be surprised into falling out of control 
through ignorance. 

The best weather for flying is obtainable on a calm, clear day, when 
eddies or vertical currents are not likely to be encountered. A strong gale 
is about the only condition that makes flight impossible to the modern aii- 
plane, although fog is a considerable handicap to military flying, by reason 
of the poor chances for proper observation. 

A ground haze, low lying clouds, and location of the sun dead ahead, 
also impede useful military flight, as do detached clouds; but none of these 
prevent the aviator going aloft. Air eddies and ascending or descending 
currents, too, are seldom so violent that flying is seriously interfered with. 
For students engaged in first flights, the early morning and evening are the 
most suitable times, for it is then that the aii is calmest. In the TJ nited States, 
winds from the east and southeast carry with them less bumps and aic 

most favorable. 


137 


138 


Practical Aviation 


CHARACTERISTICS OF THE AIR 

COMPOSITION OF THE ATMOSPHERE 

Air is a gaseous body, which, like water, seeks the level where lowest 
pressure exists. It is 1,600 times lighter than water, but it is at least 50 
miles deep, and since one-half of its weight is below 3 miles altitude, its 
weight or pressure at the earth is considerable. Its constituents are: nitrogen, 
79 per cent.; hydrogen, 20 per cent.; argon, 1 per cent. 

ATMOSPHERIC PRESSURE 

The weight of air on a given spot is atmospheric pressure. The longer 
the column of air above the place, and the greater the density of the air, the 
greater will be the pressure at the bottom of the column. 

Pressure is variable, however. The temperature of the air usually decreases with 
height at a rate of about one degree for every 300 feet. This rule is not an absolute 
one, since temperature varies with locality and season of year, but is useful as a 
general guide. Density of the air is affected by temperature, due to the expansion of 
heated air and contraction of cold; density is also affected by pressure, for the higher 
the air column the greater the air contained in a given space at the bottom. 

Air at rest is given motion by change in temperature at the earth. For example, 
heat from the sun’s rays is not absorbed uniformly, bare earth heating more rapidly 
than portions covered by trees and grass. Over the bare spot the heated column of air 
will rise by expansion, and as it rises the pressure there will be diminished, whereupon 
the cooler surrounding air will rush into the vacated space. As the operation is 
repeated the air motion increases. Thus elevations and depressions are formed, or, 
as they are termed in meteorology: HIGH PRESSURE AREAS and LOW PRES¬ 
SURE AREAS. 

MEASURE OF PRESSURE 

The barometer is the instrument used to measure air pressure. It is measured by 
the height, in inches, of a column of mercury necessary to balance it. At a fixed time 
each day atmospheric pressures taken at various stations scattered over the country are 
telegraphed to the meteorological office and a weather map is made from those reports. 
Such a map is illustrated in Figure 107. 

By joining places which register the same barometric pressure, lines are formed 
similar to map contour lines and known as isobars. 

PRESSURE AREAS 

All places on any line (isobar) have the same atmospheric pressure; where little 
difference of pressure exists at places close together, the isobars will be close together, 
and vice versa. The air forced from high pressure to an area of lower pressure does not 
follow a straight line, but takes a spiralling course in a direction more nearly parallel 
to the isobars than at right angles. This is due to the irregularities of the earth’s 
surface and the revolution of the earth on its axis. 

Pressure areas, which usually have a diameter of hundreds of miles, do not remain 
in the same position, examination of U. S. weather maps for successive days showing 
that they ordinarily move in a general easterly direction and occasionally north and 
south, but westward only in hurricanes. 

An unusually small pressure area indicates a cyclone area and sudden violent 
changes in weather may be looked for. In a high pressure region, or anti-cyclone, 
the weather to be expected and the indications are almost the reverse. 

Since the winds flow spirally about the pressure areas, the isobars on the weather 
map furnish the aviator information as to the general direction of the wind, knowledge 
which is extremely valuable if a cross-country flight is contemplated. 

CYCLONE (LOW PRESSURE AREA) 

The winds blow anti-clockwise about the center of pressure (clockwise in the 
southern hemisphere). The barometer falls with the approach of the cyclone, begin¬ 
ning to rise again after the center of the area has passed. The front of the depressed 
area usually holds rain or cloudiness, the rear cooler weather and clearing. 

ANTI-CYCLONE (HIGH PRESSURE AREA) 

An anti-cyclone has no general direction of motion, in fact it is frequently station¬ 
ary for days. The winds spiral clockwise from the center and are very light. Almost 
any type of weather may be expected except heavy winds. Ordinarily, the weather 
is fine, but in cold weather fog and low lying clouds are frequent, and rain occasional. 






139 


Characteristics of the Air 



Figure 107 —Meteorological map showing atmospheric pressures 

SECONDARY DEPRESSIONS 

Irregularities in the form of indentations in the isobars frequently appear in a 
cyclone area. These secondary formations may or may not be well defined; if marked, 
the winds may become very strong and the weather bad. In front of the secondary 
the weather is similar to the cyclone; between the secondary and main depression the 
winds are light, but very strong on the side furthest from the center of the cyclone. 

THE WEDGE 

When a series of cyclones pass across country in continuous succession, V-shaped 
isobars appear between cyclones. These indicate fine clear weather, but of short dura¬ 
tion, as another cyclone is approaching. 

LINE SQUALLS 

As the center of a cyclone passes line squalls often appear. They are usually very 
narrow hut often 500 miles in length, are very sudden and violent and, traveling 
approximately at a right angle to their length are very dangerous to airmen. The 
barometer shows a small sudden rise, and a fall in temperature is noticeable; often 
heavy rain and hail set in, and, occasionally, thunder. These squalls seldom give any 
warning and are therefore particularly dangerous. 

BEAUFORT SCALE 

Wind strength is generally expressed as velocity in miles per hour. For con¬ 
venience winds are divided into 12 groups or classifications, a system known as the 
Beaufort scale. 

BEAUFORT SCALE 



Division 

Nautical 

Description 

Division 

Nautical 

Description 

Number 

m. p. h. 

of Wind 

Number 

m. p. h. 

of Wind 

0 

Less than 1 

Calm 

7 

28—33 

High wind 

1 

1— 3 

Light air 

8 

34—40 

Gales 

2 

4— 6 

Slight breezes 

9 

41—47 

Strong gales 

3 

7—10 

Gentle breezes 

10 

48—55 

Whole gale 

4 

11—16 

Moderate breezes 

11 

56—65 

Storm 

5 

17—21 

Fresh breezes 

12 

Above 65 

Hurricane 

6 

22—27 

Strong breezes 































































140 


Practical Aviation 



Figure 108 {Upper)—Action of the aerial fountain Figure 109 {Upper)—Action of the surface cataract 

Figure 110 {Lower)—Vertical wind eddies below hill crests Figure 111 {Lower) — Eddies, or bumps, in lee of obstacles 





















































































Wind Columns, Eddies and Gusts 


141 


WIND CONDITIONS WHICH AFFECT AVIATION 
WIND DISTRIBUTION 

The aviator does not need to study the cause of wind, but he should 
know something of its distribution. Wind is stronger by day than by night at 
the earth’s surface; its average velocity in the United States is 11 miles per 
hour, normally increasing with altitude up to 1,000 feet, above which height it 
“veers,” or goes round in a clockwise direction. 

The following condensed scale is useful for calculating wind problems: 

At 1,000 feet wind velocity increases 1^4 times, with 10 degree veering. 

At 2,000 feet velocity nearly doubles and wind veering is 15 degrees. 

Above 3,000 feet velocity is double and there is practically no further increase and 
veering is constant at 20 degrees. 

AERIAL FOUNTAIN 

A rising current of atmosphere encountered over barren land and conical hills in 
warm weather, the air column rising because it is heated beyond the temperature of the 
surrounding air. These fountains are not ordinarily dangerous but the rate of ascent 
has been known to reach a velocity of 25 feet per second. The airplane will rise invol¬ 
untarily if caught squarely by one of these columns, dropping as it emerges. Wing 
tips will be tilted if the aerial fountain is grazed. See Figure 108. 

AERIAL CATARACT 

Descending cold air causes a current which takes two forms (a) the reverse of the 
aerial fountain with opposite effect on airplanes, and dangerous only in thunder storms; 
(b) surface cataracts developed by steep barren slopes of earth. The action of the 
surface cataract is shown in Figure 109. Landing should never be attempted in a 
surface cataract. 

AERIAL CASCADE 

The bounding air at the bottom of a steep fall over an earth contour is similar to 
the result with a water cascade. Eddies of a treacherous character are set up, and 

counter currents, above which the aviator must remain for safety. 

AERIAL BREAKERS 

Strong cross currents form choppy winds with action similar to ocean breakers. 
These are generally heralded by corrugated clouds and are to be noted as difficult of 
navigation by air pilots. 

VERTICAL WIND EDDIES 

Below the crests of hills wind eddies form, which describe circles in the vertical 
plane. See Figure 110. Should the aviator be caught in the pocket under a hill the 

airplane should be headed in and a landing made parallel to the side of the hill. 

WIND LAYERS 

Wind will very often be found blowing in different directions and velocities at 
different heights. Although horizontal, passing from one layer to another of different 
speed and different direction momentarily changes the buoyancy of the airplane, causing 
the machine to rise or fall. Turbulent motion and a few bumps will only be expe¬ 
rienced, and wind layers are therefore not ordinarily dangerous. 

WIND BILLOWS 

These are horizontal billows similar to ocean waves and occur at the surface 
between wind layers; rough going, not necessarily dangerous, results. 

WIND GUSTS AND EDDIES 

These are generally known in aviation parlance as “bumps.” Obstacles in the path 
of moving air at the surface cause them. They are strongest on the leeward side of 
hills, buildings, or other elevations, and most noticeable in a strong wind. Figure 111 
illustrates the action of the air. If landing is forced, the aviator should select the 
windward side of the obstruction or a point well away to leeward. 

AERIAL TORRENTS 

The aerial torrent is caused by air colder than the surrounding air pouring down¬ 
ward. Great velocity is attained on surface slopes or open valleys. The effect on the 
airplane is exactly opposite that of the aerial fountain illustrated in Figure 108. 








142 


Practical Aviation 



Figure 112 —Cirrus {Mare’s Tails'), alti¬ 
tude 30,000 feet or more. Predict zuind 
and cyclonic depression 



Figure 115 —Nimbus (rain cloud), alti¬ 
tude 300 to 6,500 feet. Steady rain or 
snow usually falls 



Figure 113 — Alto-Cumulus; 
10,000 to 23,000 feet. Indicate 
cross currents of air 


altitude 

strong 


Figure 116 —Cumulus {woolpack clouds), 
altitude 4,500 to 6,000 feet. Cause zno- 
lent disturbances to the airplane 



Figure 114— Strato-Cumulus; altitude 
6,500 feet. Large globular masses or 
rolls, frequently covering whole sky. 
Predict a change in weather 


Figure 11 7 — Cumulo-Nimbus (thunder 
cloud), altitude 4,000 to 26,000 feet. Dan¬ 
gerous to aviators because of strong 
currents and electric effects 




























Weather Forecasting by Clouds 


143 


CLOUDS AND THEIR SIGNIFICANCE 


CLOUDS 

Clouds are formed, (a) by condensation when an ascending mass of 
moist air encounters another moist mass of different temperature; (b) by 
cooling, when an ascending column of vapor, mixed with particles of dust, 
condenses. Types of clouds and their direction indicate the weather to the 
observing aviator. Clouds are either in the form of sheets or heaps, and may 
be so studied. 

CLASSIFICATION OF CLOUDS 

Cirrus—(Mare’s Tails.) Light wisps of whitish cloud, of fibrous appearance with 
no shadows. These clouds are the highest in the international classification, commonly- 
appearing at an altitude of 30,000 feet or more. They predict wind and a cyclonic 
depression. Illustrated in Figure 112. 

Cirro-Stratus—A thin sheet of tangled web structure, whitish, and sometimes 
covering the sky completely, giving it a milky appearance. This cloud often creates sun 
and moon halos. Its average height is 29,500 feet. Forecasts bad weather. 

Cirro-Cumulus—(Mackerel Sky.) Small globular masses or white flakes without 
shadows, or showing very light shadows, arranged in groups and often in lines. Aver¬ 
age height between 10,000 and 23,000 feet. Denotes fine weather. 

Alto-Stratus—A thick sheet of gray or bluish color, sometimes forming a compact 
mass of dark gray color and fibrous structure. Often causes brilliant coronae when 
near sun or moon. Average height 10,000 to 23,000 feet. 

Alto-Cumulus—Large globular masses, white or grayish, partially shaded, arranged 
in groups or lines, and often so closely packed that their edges appear confused. 
Illustrated in Figure 113. This cloud formation is somewhat similar to the.mackerel 
sky (cirro-cumulus); it has the same elevation, 10,000 to 23,000 feet. The cross lines 
indicate strong cross currents of air. 

Strato-Cijmulus—Large globular masses or rolls of dark clouds, frequently covering 
the whole sky, especially in winter. Altitude 6,500 feet. Illustrated in Figure 114. 
Predict a change in weather. 

Nimbus—A thick layer of dark clouds without shape and with ragged edges from 
which steady rain or snow usually falls. Shown in Figure 115. Through the openings 
an upper layer of cirro-stratus or alto-stratus is almost invariably seen. Low elevation, 
300 to 6,500 feet. 

Cumulus—(Woolpack Clouds.) Thick clouds of which the upper surfaces are 
dome-shaped with protuberances; base horizontal. Illustrated in Figure 116. They indi¬ 
cate the aerial fountain and are low flying, 4,500 to 6,000 feet. Violent disturbances to 
the airplane will be experienced when passing through them, or passing above or below. 

Cumulo-Nimbus—(Thunder Cloud.) Heavy masses of cloud rising in the form of 
mountains or turrets or anvils, generally surmounted by a sheet or screen of fibrous ap¬ 
pearance (false cirrus) and having at its base a mass similar to nimbus (rain cloud). 
Illustrated in Figure 117. Apex 10,000 to 26,000 feet; base, 4,000 feet. Dangerous to 
aviators, because of strong currents and electric effects. 

Stratus—A uniform layer of cloud which resembles fog but does not rest on the 
ground. It usually is stationary or drifting slowly at altitudes of 100 feet to 3,500 feet. 


GENERAL OBSERVATION 

Aviators may gain valuable knowledge of existing wind currents by 
observation of clouds. The general rule is that unbroken clouds indicate 
smooth, even air flow, broken formations the presence of air currents. The 
behavior of these currents may be anticipated by applying the above class¬ 
ification to the clouds in evidence. 





144 


Practical Aviation 



A good illustration of how an airplane may drop to dangerous levels when coming out of an 

aerial fountain 
















Practical Aviation 


145 


REVIEW QUIZ 

Meteorology for the Airman 

1. In what way is ability to apply the laws of weather forecasting a 

safeguard for the aviator? 

2. Why are calm, clear days best for flying? 

3. From which direction do winds carrying least “bumps” blow in the 

United States? 

4. State the percentage of air weight below 3 miles altitude. 

5. Define atmospheric pressure. 

6. Describe the processes by which air at rest is given motion. 

7. What instrument measures air pressure? 

8. How are pressure areas indicated on weather maps, and how can 

the aviator secure valuable cross-count-y flight data from these 
indications? 

9. State the difference between high and low pressure areas and give 

another meteorological term to describe them. 

10. What weather is indicated by wedges? 

11. Explain why line squalls are dangerous to airmen and give the 

barometer indications. 

12. State the velocity increase and veering of wind at 1,000, 2,000 and 

3,000 feet. 

13. Define an aerial fountain and its action on an airplane entering, 

leaving and grazing it. 

14. Why should aviators avoid landing in aerial cataracts? 

15. Explain the action of a vertical wind eddy and how a landing in 

such should be made. 

16. Give two convenient classifications of cloud forms. 

17. Name and describe a type of cloud which predicts bad weather. 

18. Give the name and appearance of a type of cloud which denotes 

fine weather. 

19. Name and define four cloud formations which indicate winds un¬ 

favorable to flying. 

20. State a general rule for distinguishing smooth air from that with 

cross currents by observation of the clouds. 






146 


Practical Aviation 


CHAPTER ANALYSIS 

Aerial Gunnery and Combat 
Bombs and Bombing 


COMBAT AIRPLANES: 

(a) Function. 

(b) Employment. 

FACTORS OF SUCCESS IN 
AIR COMBAT: 

(a) Airplane Superiority. 

(b) Strategy. 

(c) Aerial Gunnery. 

THE LEWIS MACHINE GUN: 

(a) General Description. 

(b) Operating the Gun. 

(c) Loading. 

(d) Firing. 

ACCURACY AND VOLUME 
OF FIRE: 

(a) Accuracy. 

(b) Volume. 

(c) Firing at Ground Targets. 

AMMUNITION AND FIRE 
CORRECTION: 

(a) Types of Bullets. 

(b) Correction of Fire. 

GUN MOUNTINGS AND 
FIRE RADIUS: 

(a) Forward Gun Mountings. 

(b) Effective Angles of Fire. 

FIGHTING IN THE AIR: 

(a) Skill in Attack. 

(b) Methods of Attack. 


AERIAL TACTICS: 

(a) Flying in Formation. 

(b) The Start. 

(c) The Flight. 

(d) Signals in Formation. 

(e) Employment of the Air Fleet. 

(f) Theory of Concentration. 

(g) Warfare Altitudes. 

(h) Tactical Skill. 

CONTACT PATROL: 

(a) Scope of the Observation. 

(b) Trench Offensives. 

ANTI-AIRCRAFT FIRE: 

(a) Action Under Fire. 

(b) Location and Types of Guns. 

(c) Shell Trajectories and Ballis¬ 

tics. 

(d) Defending Positions. 

(e) Attacks on Balloons. 

BOMBING AIR RAIDS: 

(a) Types of Bombing Airplanes. 

(b) Mufflers and Flares. 

(c) Training Bombing Crews. 

TYPES OF BOMBS: 

(a) Incendiary Bombs. 

(b) Safety Devices. 

(c) Explosive Bombs. 

(d) Bomb Carriers and Launch¬ 

ing Cradles. 

(e) Steel Darts. 

BOMB DROPPING: 

(a) Range Finders. 

(b) Operation of the Range 

Finder. 




CHAPTER XIV 


Aerial Gunnery and Combat—Bombs and Bombing 

Combat airplanes, known variously as pursuit, chaser and fighting planes, 
have as their main duty the securing of superiority over the enemy in the 
air, or mastery of the air. Clearing the skies of hostile airplanes over the 
theatre of operations requires domination of the air situation, repulsing all 
efforts of the enemy to make observations of troop movements or occupied 
positions, frustrating all bombing raids or other air offensives, and insuring 
the success of these missions over enemy territory. 

The work roughly divides itself into: (a) patrolling, (b) sentinel duty. 

Patrols comprise those for interior and exterior duty. 

Driving the enemy out of the air in a given sector is accomplished by 
the fast machines of the air squadron, speedy pursuit planes taking the air 
singly or in small bodies and following the hostile airplanes to the distance 
dictated by the strategic situation and the co-ordination with supporting air¬ 
craft. Patrols are continuous when weather permits, and the aviators se¬ 
lected for this duty are the pick of the service, all being skilled in air acrobacy 
which is extensively employed in aggressive and defensive fighting. These 
fighters seek combat at every opportunity, often cruising about singly or in 
formation in a roving search for hostile fliers. At other times a definite 
mission is determined in advance, perhaps to engage enemy airplanes which 
have been observed, or to seek certain areas over which hostile air forces 
are expected. Again, the objective may be the destruction of enemy captive 
observation balloons, a particularly dangerous duty owing to the protection 
afforded these by battleplanes and anti-aircraft batteries. 

Maintenance of an aircraft screen is the essential of sentinel duty. Aside 
from special missions, the fast combat planes are assigned to definite air 
lanes or areas 5,000 to 7,000 feet above the reconnaissance and fire control 
airplanes, the fighters supplying protection to the slower observing craft 
operating at 2,500 to 3,000 foot altitudes. Beating off hostile air attacks 
is accomplished according to the requirements of the situation, supporting 
combat craft closing in at the point of attack. Pursuit of enemy airplanes 
requires an extension of patrol lanes by the machines remaining behind, for 
at no time must the observers be left unprotected. 

Combat planes are well armed and placed in the hands of the most 
skilled and quick-witted aviators. Their’s is a great responsibility, for they 
not only afford the observing planes protection over the enemy lines, but 
ward off attacks on friendly observation balloons four or five miles back 
within their own lines and also accompany daylight bombing missions to 
engage attacking planes. 

Contact patrol, or co-operation at low altitudes with infantry in assault, 
is still another function, for which great skill is demanded. Expertness in 
use of the machine gun, thorough familiarity with acrobatics and dauntless 
courage are the requisites of the aviator given a combat plane. 

147 



148 


Practical Aviation 














Value of Technical and Strategical Superiority 


149 


FACTORS OF SUCCESS IN AIR COMBAT 

Success in airplane fighting is not a matter of luck or due to the un¬ 
reasoning type of dare-devil assault. Cool calculation and application of 
carefully defined principles of strategy and tactics is responsible for prac¬ 
tically all victories. 

fhe personal equation, always a great factor in success with arms, looms large 
in air combat. Aggressiveness must be combined with agility of mind and technical 
skill is of the utmost importance. 

A third advantage rests with superiority in equipment, notably the speed, climbing 
and maneuvering ability of the airplane, its armor and the number and type of guns 
comprising its armament. 

AIRPLANE SUPERIORITY 

Engaged singly in combat, it is obvious that the advantage lies with the airplane 
which has the greatest mobility of movement, being enabled by superior speed, climb 
and flexibility to out-maneuver its opponent. The air-worthiness, or flying qualities, 
determine which machine will emerge from circling and diving to the most favorable 
position, either above, below, in rear or advance of the enemy craft, advantages de¬ 
termined by tactical considerations such as type, armament, number and disposition 
of the hostile craft. Choice of position is largely governed by the type of airplane. 

Tractors are ordinarily armed with two machine guns, operated either by the pilot 
or gunner, or both. With the pilot in the front seat, the gunner has a wide arc of fire 
to the rear, but with the pilot in the rear the gunner is in full observation and the 
machine is best maneuvered for direction of fire. Mounting the machine gun on the 
top plane permits operation from the rear seat; it therefore has obvious advantages. 
As combat airplanes are essentially of the pursuit type, the most effective fire should 
be to the front. 

Pusher types are generally at a disadvantage because of inferior speed. But with 
the gunner placed well forward in the nacelle a wide arc of lateral and vertical fire is 
obtained. For heavier armament the pusher type has undoubted superiority, but in 
firing backward through the propeller efficiency is lost. Exception must be made in 
the double propeller pusher types where the arc of fire is clear, but although both 
tractor and pusher have separate advantages and both have many advocates, the speed 
and mobility of the tractor type give it a definite point of superiority. 

STRATEGY 

Familiarity with the appearance of various types of enemy airplanes, which is 
essential knowledge to the military aviator, includes an estimate of their speed and 
mobility, number, disposition and range of guns, and the best means of attacking in 
each case. 

The former “blind spot,” i.e., under the tail, is now defended by a machine gun 
which shoots through a tunnel in the fuselage; thus the approach from the rear, firing 
upward, is no longer a fundamental principle of attack. Clouds and the sun may be 
usefully employed; for to get between the enemy and the sun blurs the outline of the 
approaching plane. Hiding behind clouds and diving carries the element of surprise 
and is widely employed. 

Acrobacy is an essential accomplishment, for a general rule governing air combat, 
in event of failure in surprise attack, is to duplicate every movement of the enemy 
engaged. If a diving attack is made the adversary dives, looping or zooming before 
the hostile machine guns are within range, thus reversing the position and gaining the 
altitude advantage. The same is true of climbing; the pursuer also climbs, attempting 
by superior climbing ability to reach a position where he can dive at his opponent. 
Short rises and dives in quick succession constitute an effective form of attack on a 
machine armed with two or more guns. Direct hits by machine gun fire are difficult 
of accomplishment and, due to the frequent misses, air combat remains largely a 
matter of skilful acrobacy. The operation of the airplane must be instinctive with the 
fighting aviator, aerial evolutions being accomplished without a second thought, so the 
greater concentration may be given to accuracy of fire. 

Jamming of machine guns is frequent, often occurring at the crucial moment, and 
temporarily disarming the fighting pilot; a quick escape is then required. This can 
seldom be effected by straight-away flight at high speed toward friendly territory, 
owing to the target the machine will thus present. Side slips and spins, in fact all 
forms of aerobatics which give the appearance of an airplane falling out of control, are 
resorted to, the machine being straightened out when well out of range. At all times, 
therefore, the fighting aviator must know his position in reference to his own lines, 
for aerial combat may take him many miles within enemy territory. An aviator is 
ordered to take no chances when odds are against him, and strategy demands that an 
escape be attempted if anything goes wrong with his machine or gun. 




150 


Practical Aviation 





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Description and Operation of Machine Gun 


151 


THE LEWIS MACHINE GUN 

This weapon is a standard airplane arm, weighing about 16 pounds, 
simple in action and with comparatively few parts. Success in its handling 
is largely dependent upon the operator’s familiarity with the piece. The 
fighting aviator should have full knowledge of all parts of the gun and be 
able to dismount, assemble and adjust it without stopping to think about 
the process. To recognize, instantly, any fault in its operation while firing 
and to correct it without hesitation is, broadly speaking, the skill required. 


GENERAL DESCRIPTION 

The Lewis machine gun is air-cooled gas operated, and magazine-fed. 
The magazine is a circular drum in which the cartridges are arranged radially; 
the bullet ends are toward the center and are engaged by a spiral groove 
in the magazine center, down which the cartridges are driven until they 
are successively reached by the feed operating arm. While firing the other 
parts of the magazine are rotated about the center. Gas pressure, produced 
in the barrel by the exploding cartridge, furnishes the motive power for 
operating the mechanism. This gas, drawn into a cylinder through a hole 
near the muzzle of the barrel, drives a piston back, and thus winds the main¬ 
spring which operates the breach bolt and ejector, feeds a new cartridge, 
and rotates and locks the magazine. If the trigger is held back the firing 
is continuous until the magazine holding 100 cartridges has been emptied. 
To fire a single shot the trigger is pressed and released immediately. 
OPERATING THE GUN 

By constant reference to the drawing of the Lewis gun in section, Figure 113, the 
reader will understand its operation in detail from the following description: 

Loading—The charging handle (see slot at rear of 8-1 Rack on drawing) is placed 
in full forward position, the magazine placed on its post and pressed down, thumb 
piece of magazine latch to right. The charging handle is then drawn back fully until 
it is engaged and held. This draws back the piston, drawing the rack teeth over the 
teeth of the gear (9-7) which rotates the gear and winds its mainspring. During the 
rearward travel, the striker (8-2) has been drawn back from the face of the bolt and 
the bolt rotated from right to left, turning the locking lugs out of their recesses. As 
the bolt is unlocked the striker post carries it back with it. The feed operating arm 
is swung across the top of the receiver by the feed operating stud (4-1); and the feed 
pawl (7-2), acting against one of the outer projections of the magazine pan, carries 
the magazine around sufficiently to drive the first cartridge down the spirally grooved 
center into the opening in the feed operating arm. This is the position pictured in 
the drawing, Figure 118. The feed operating arm brings the cartridge under control 
of the cartridge guide and a spring stud clears the stop pawl, which presses forward 
and prevents further rotation of the magazine. Meanwhile the rear end of the bolt 
has driven the ejector into its slot, and the rear end of the piston: rack has set the sear 

spring which cocks the piece. . 

Firing When the trigger is pressed, the sear is drawn out of engagement with 

the notch in the rack, the latter being then drawn forward by the unwinding of the 
mainspring, rotating the gear in mesh with the rack. , 

In the forward motion of the bolt a stud cams the feed operating arm to the right, 
a spring stud on the latter pressing the stop pawl back from the magazine projection; 
the head of the bolt now presses the ejector into its cut and the face of the bolt, 
striking the base of the waiting cartridge, takes it from the loading ramps of the 
receiver and drives the cartridge into the chamber. The extractors spring over the 
rim as the cartridge seats. The bolt locking is completed by the forward motion ot 
the striker post, which then enters the front part of its cut, carrying the striker against 

the cartridge primer and firing it. c . » 

The firing of the cartridge develops the power for another cycle of operation. As 

the eas which drives the bullet forward reaches near the muzzle of the barrel it is 
driven down through a hole into the gas chamber (3-34). Thence it passes under 
pressure through a hole, striking against the head of the piston and driving it back. 
This backward movement produces the movements of loading as described above 
The empty shell, however, in the grip of the extractors is drawn back with the bolt, 

throwing the shell out of the ejector port. . . . , , r 

If the trigger is held back the gun will fire again and continue the cycle of opera¬ 
tions at the rate of about 10 shots per second until the magazine is empty. 



152 


Practical Aviation 



Figure 119— The ditch target; Figure 120— The moving target for ground practice, 
a splash records a hit showing the armor shield for the operator 

ACCURACY AND VOLUME OF FIRE 


Engagements between airplanes in combat are brief; thorough training 
in aiming and delivering machine gun fire is therefore given a prominent 
place in instructing the aviator. Gunnery skill is the deciding factor between 
opponents with equal technical advantages and flying ability, and at all times 
has considerable bearing upon victory or defeat. 

ACCURACY OF FIRE 

Due to aiming at a constantly moving target from a generally unstable base, ac¬ 
curacy in fire is seldom reduced to exactness. Distinct superiority in aiming may be 
acquired, however, by diligent practice on simulated moving airplanes, and is worth 
all the effort which may be given it. 

VOLUME OF FIRE 

High rate of fire is essential to an airplane arm, since the range is of limited 
length and the duration of effective fire reduced to a few seconds. The machine gun 
which operates at greatest rapidity and with smoothest action gives a decided ad¬ 
vantage, owing to the limitations in accuracy of aiming. 

FIRING AT GROUND TARGETS 

Two types of targets are illustrated in Figures 119 and 120. In Figure 119 a circle 
of sand is shown with two intersecting ditches in the form and size of an airplane, 
filled with water so a splash registers a hit. An observer under cover watches and 
records the number of times the target is struck. The airplane illustrated has the 
gun mounted rigidly on the upper plane and the entire machine is aimed at the mark. 
A flexible cable connects the gun trigger to a lever on the control stick, the gun firing 
as the lever is squeezed. An open sight on a level with the pilot’s eyes is used for 
aiming. 

An advanced instruction device on the same principle utilizes a cross which re¬ 
volves on a bar, describing a 40-foot circle. It is operated from a protected trench 
by means of a cable and pulley which rotates the target at the approximate speed of 
an airplane in a spiral. The shots are made at a height of about 800 feet above the 
ground. 

Figure 120 clearly illustrates another form of moving target, the truck being 
operated by the man seated behind the armored shield. Students fire at the moving 
outlines of the airplane from the ground, either from a stationary seat or from the 
pivoted chassis shown in the photograph below, a representation of an airplane cock¬ 
pit which sways at the slightest movement. 



























































Bullet Types and Fire Correction 153 



r t I Kr v u\j / u \j I x - x^w r i ^ 11 wi* in ix i ^ r r c y, t 

AMMUNITION AND FIRE CORRECTION 


Correction of machine gun fire is commonly made by observation of the path of 
phosphorous tracer bullets, placed about every fifth position in the magazine. The 
gun is deflected, raised, or aimed to either side, in accordance with the direction of 
the smoke trail toward the enemy airplane. The objective is usually the back of the 
pilot, aiming being governed by its appearance in the center of the sight. Various 
types of bullets are used in machine guns and an understanding of their functions and 
construction is useful. 

TYPES OF AMMUNITION 

The five common types of bullets for air warfare are illustrated in section in Figure 121. 

ORDINARY—The head of this bullet is usually of solid brass and presents no new features. 

PERFORATING—This type of bullet is designed to pierce metal, being used against airplane motors 
and fuel tanks. The core is ordinarily of hard steel encased in a covering of copper, zinc and nickel alloy. 

TRACING—These bullets are hollow and filled with a phosphorous compound; the casing io an 
alloy of copper, zinc and nickel. They leave a luminous or smoke trail behind and are combustible; they 
are designed both for fire correction and for incendiary purposes. 

EXPLOSIVE—The bullets are made somewhat in the form of a small shell; they are hollow and 
contain an explosive charge in the nose, consisting of chlorate of potash and sulphur, in equal parts, acting 
both as detonator and exploder. The lighter, flattened nose gives this type of bullets a different trajectory 
from those of ordinary form. 

EXPANDING—Destruction of struts and spars is the mission of the expanding type, drilled at the 
nose so instantaneous disintegration takes place even when encountering small diametered parts of low 
density. 

CORRECTION OF FIRE 

While several formulae have appeared to determine accuracy of aiming at hostile 
machines, practical application is well nigh impossible because they presuppose a 
knowledge of (a) speed of both airplanes, (b) aiming angle with reference to flight 
path, (c) enemy machine’s flight path. The hopelessness of determining these is 
immediately apparent without proper instruments; dependence is therefore placed 
upon the trail of the tracer bullet, although special apparatus for sighting which makes 
an automatic correction has been developed, but must not be described just now. 

A few principles of sighting upon which correction calculations are based are illus¬ 
trated in the diagrams, Figures 122, 123 and 124. The only correction necessary in the 
case of Figure 122 is a raising or deflection of the gun or the airplane A, according to 
whether gun is fixed or movable. 

In Figure 123, enemy airplane B has a course at a wide angle to the path of A. Since 
the enemy machine is moving forward at high velocity, it is necessary to aim on the line 
A, C, the measure of correction being the line B, C. 

Figure 124 illustrates the principle which depends upon the angle of the gun with 
reference to the flight path, it being necessary in this, case to .make allowance for the for¬ 
ward motion of both machines, aiming at an approximate point C, instead of directly at 
at enemy airplane B. 































154 Practical Aviation 



• I 




Figures 125a —Gun fixed on upper plane Figure 125 b—Firing through propeller 




Figure 12 7a—Effective lateral arc of Figure \27b—Effective longitudinal arc of 
rear gun rear gun 



Figure 129 a—Joining arcs of two mobile guns Figure 129b—Longitudinal radius of action 






























































Values of Various Gun Arrangements 


155 


GUN MOUNTINGS AND FIRE RADIUS 

Placing of machine guns and their number on enemy airplanes is a matter for 
exact knowledge with the military aviator. From recognition of a type he can estimate 
his chances of evading its lire and the best points of attack. 

The various arrangements of armament of hostile airplanes becomes thoroughly 
familiar in sectors where daily engagements are the rule, and although distribution 
and number of machine guns are subject to constant change, acquaintance with the 
field of fire and mobility of the various arms establish certain principles which arc 
fundamental and determine the possibilities of all modifications. Account must be 
taken of the value of surprise in arranging armament. A brief discussion of the effec¬ 
tive fire secured by the various arrangements follows: 

FORWARD GUN MOUNTINGS 

The first consideration in placing forward guns in tractor types is their location. 
Figure 125-a illustrates the machine gun fixed to the upper plane and firing over the 
propeller; Figure 125-b gives the arrangement for firing through the propeller, as 
usually placed in one-man airplanes. Placing the gun on the top plane has two disad¬ 
vantages: Resistance to the air, increasing the drift and consequently lessening lift, 
and difficulty in reloading the gun. To remove the empty magazine and replace it 
with a loaded one requires turning the gun upside down. When it is considered that 
the rate of fire is so rapid that the magazine is emptied in 10 or 15 seconds, it is 
obvious that unless a hit is made with the emptying of the first magazine the airplane 
is helpless in the matter of further immediate attack. 

Shooting through the propeller is accomplished by synchronizing the discharge 
of the gun with the revolutions of the propeller, the mechanism being governed by 
the motor. The device is timed to suspend discharge when the blades are passing the 
muzzle of the gun; thus with a propeller revolving at the rate of 1400 r.p.m. the two 
blades pass that point at intervals cf 1-47 of a second, a fraction of time which has 
no material bearing upon maintenance of virtually continuous fire. 

Armoring the propeller blades to deflect the bullets is another method which has been employed, but 
is not favored to as great an extent as synchronizing. Triangular pieces of hard steel set in the blades 
at the point of the bullets’ path save the propeller from breaking, under this method, and deflect the bullets 
striking them, the percentage of loss being negligible, as low as 5 to 8 per cent. Tapering the propeller at 
the point of the steel plate inset, however, means a loss in tractive efficiency, lessening airplane speed 
as much as 12 miles per hour, a consideration of so great importance as to make the method inferior to 
the synchronizing application. 

EFFECTIVE ANGLES OF FIRE 

The various arrangements of machine guns pictured on page 154 are worthy o r 
careful study by the military aviator. 

Figures 126-a and 126-b show the application of a single forward gun to an airplane 
of pusher type, the weapon being pivoted in the front of the nacelle. 1 he clotted 
lines show the limitations of the lateral and longitudinal arcs of effective fire, and the 
shaded portions the considerable dead area behind, the sides and rear being particular 
points of vulnerability. 

Figures 127-a and 127-b illustrate the placing of a gun in the cockpit of a tractor 
machine, giving it a wider arc of effective fire to the sides and above and below, but 
still leaving considerable dead area in front. The fact that this blind, or undefended, 
spot is in full view of the pilot who is maneuvering the machine makes it less vul¬ 
nerable than in the case of Figure 126. 

Figures 128-a and 128-b show the tractor airplane with the addition of a forward 
gun shooting through the propeller. The arc of fire- of this gun is governed by the 
mobility of the airplane, that is, its radius of effective action depends upon the skill 
of the pilot and the machine’s maneuvering ability in his hands, since the _ gun is 
pointed by the change of direction in the entire airplane. As this gun is mainly for 
offensives, the rear gun’s function is principally defensive, a wide arc of fire to the rear 
enabling it to ward off attacks from many directions. This arrangement of guns is 
generally found on light bombing and reconnaissance or fire control machines. 

Figures 129-a and 129-b illustrate the effective armament of either tractor or 
pusher types having two propellers. These machines are largely used for bombing 
and protection of aircraft or military bases, the armament being of great defensive 
value Airplanes of this class with tractor screws are armed with the additional gun 
shooting through a tunnel under the fuselage already referred to. In type of machine 
many modifications appear, but this form of armament is general with practically 
all airplanes carrying three or more men. 








156 


Practical Aviation 



Figure 130 —How a supporting airplane remains hidden from an attacking enemy 



Figure 132 —The usual method of formation attack on a single enemy 































Methods of Attack and Combat Rules 


157 



Figure 133 —The steep Figure 134 —Employing the Immelman turn to effect an 
angle for dive attack escape from an attack in formation 

FIGHTING IN THE AIR 

Pilots of combat airplanes must be physically fit and mentally alert at all times. 
The enemy’s qualifications for success are fully as great, and success is gained only by 
dauntless courage governed by quick-witted application of flying and gunnery skill. 
The following principles governing individual actions in combat are to be observed: 


SKILL IN ATTACK 


As in all forms of military science, surprise contributes largely to success. The 
surprise attack is best delivered from a position between the enemy craft and the sun. 
Diving on the tail is the favored method. 

While diving, the rear should be watched; another enemy airplane may be above. 

Except when coming to the assistance of friendly aircraft, speeds below 100 miles 
per hour should be employed, as excessive velocities make the airplane difficult of 
control and the period for machine gun fire too brief. 

Fire should be withheld until within 100 yards of the enemy; the glove on the 
trigger hand is usually removed. 

The machine on top has the advantage. Attack from behind is most effective; 
right angle fire is second choice, and attacking from in front the least effective method. 

When the enemy airplane has superiority of speed the dive attack is used. If the 
hostile machine is inferior, the dive is made to his rear to a point a trifle below his 
tail; before opening fire flying speed is equalized by throttling the motor. 

Careful survey of the sky should be made before attacking a single enemy air¬ 
plane flying at a low altitude, as it may be a decoy. 

The tail is the most vulnerable spot of the airplane; attacks may be delivered and 
expected most frequently at this point. 

A one-man machine should not return to combat with a two-seater if the larger 
enemy craft has the position advantage when it opens fire. 

When flying in formation superiority of numbers decides the advisability of attack; 
position in formation lost in combat should be regained at the earliest opportunity. 


METHODS OF ATTACK . . . w . 

Fieures 130 to 133 show some forms of air tactics in combat. Figure 130 illustrates a common 
method of support, airplane B remaining above clouds ready to assist airplane A which is engaged in 
combat with enemy E, or to attack any plane coming to the assistance of E. 

Attack on an airplane which has encountered a hostile formation is illustrated in Figure 131. The 
sin-le enemy is surrounded and attacked from all sides, the leader of the formation remaining at a higher 
altitude and suddenly diving on his tail with a burst of machine gun fire. . 

The method usually employed for attack on a single enemy by three airplanes flying in formation is 

eti r \A/n in Figure 132 Planes A B and C are discovered by enemy E, who immediately dives to escape. 
The leaderA opens the attac:< by diving. Missing fire, he turns off to the left (path A1-A2). Airplane 
i . 300 feet behind at slightly higher altitude, dives and fires; missing he turns off right at B2, 

living the remaining Plane of the formation C, in a steeper dive, to intercept the enemy at E3. 

leaving i e » f rom a super ior force by diving is seldom resorted to unless the lone machine has 

" «„nJrinritv in diving speed. The usual method of getting away is by resort to air acrobatics, 
FWe 134 illustrating how the Immelman Turn can be successfully employed under the circumstances. 
* * Figure 133 demonstrates the steeper diving angle required of the attacking airplane when the adversary 

is also diving. 










158 


Practical Aviation 



Figure 135 —An American squadron flying in V-formation 

FLYING IN FORMATION 

Offensive combat in the air is seldom sought by a single airplane, well- 
defined and planned attacks against definite objectives generally being con¬ 
ducted by groups of machines, known variously by the terms wings, squadrons 
and fleets, according to their composition and numbers. The V-formation, 
illustrated in Figure 135, presents many advantages and is almost universally 
employed for air offensives. 

In this arrangement the leader, who has the point and is in command, may keep 
all the machines easily under observation and his signals are seen without effort by all 
the pilots. The stations are determined in advance and each pilot takes his assigned 
position as close as possible to the other machines and slightly higher than the air¬ 
plane immediately ahead. The formation is copied from the flight of birds, the aero¬ 
dynamic reason for its adoption being that the air in the wake of an airplane has a 
downward motion unfavorable to flight, whereas the vertical character of the air 
stream to both sides of the leader has residuary upward motion. A military reason 
for the V preference over a possible diamond-shaped arrangement, is that in the latter 
three airplanes in the rear would be open to attack instead of two. 

THE START 

Upon the leader rests the responsibility of choosing pilots and machines suitable 
for flying in one formation. As a general rule it is important that each aviator take 
aloft an airplane with which he is entirely familiar. The machines and their pilots 
are assembled some minutes before the time set for the start, their clothing and 
equipment known to be proper for the mission, pilots seated and all engines running 
throttled down, before the leader takes to the air. 

Once the leader is off the ground the other airplanes follow as near as possible 
in their formation order at intervals of 15 seconds. Attaining a height of 600 to £00 
feet in straight-away flight, the leader throttles down and watches the others pick up 
formation. This should be accomplished at a maximum rate of about a half-minute 
per man. By rocking his airplane laterally, the leader then signals attention—at 
night a red light is fired from a Very pistol—and the climb is begun. If a turn is re¬ 
quired to head in the direction of the objective, it is made in advance of the climb and 
before the motor is opened up. 

THE FLIGHT 

Constant watchfulness of the progress of his formation is required of the leader; he verifies the posi¬ 
tion of each airplane by looking around at intervals of one minute or less. The speed of the leader in 
climbing must be adjusted to the slowest airplane in the formation or the flight will be ragged from 
the beginning. Since speed is of paramount importance in air tactics, not only must the machines in 
formation be carefully selected for equal flying qualities but every pilot must hold his position with greatest 
possible exactness. Dropping out of place tends to slow up the progress of the entire formation and loss 
of position is for each individual a matter of grave importance. 

Turning is done at a signal from the leader, who rocks his airplane repeatedly and pauses; he then 
turns in the desired direction in a small arc, throttling his engine and nosing down a trifle. Assume the 
turn to be to the right. The airplanes following on the right arm of the inverted V are throttled down 
and execute at slower speed a slight turn left, turning right when the leader has turned; meanwhile 
those on the left have successively made right turns with the motor on full. When all have turned the 
leader verifies the alignment and resumes full speed ahead. 

Lateral rocking of the airplane is the attention signal. 

Waving the arm and the direction it points indicates enemy aircraft. 

The attention sienal followed by rocking longitudinally signifies a machine gun jam. 

While over hostile territory the difficulties of remaining in position are increased by anti-aircraft gun¬ 
fire and the formation is often broken; but since success in attack is largely governed by the leader’s 
freedom from concern about his force holding together, all pilots should regain position at the earliest 
moment. Constant vigilance should also be directed to preventing surprise attacks on the two rear airplanes. 













Tactical Fundamentals and Calculations 


159 


EMPLOYMENT OF THE AIR FLEET 

The plan of action is generally given to all pilots before a formation 
takes the air. Each man is expected to know his part in attainment of the 
objective and the leader’s decision on the best method of attacking a hostile 
air force when sighted must be transmitted quickly by pre-arranged signals. 

THEORY OF CONCENTRATION 

Superiority of numbers is the general indication of the probability of success, 
although estimate of speed and armament of the enemy must be taken into account, 
along with the altitude advantage. Despite the growing tendency to the use of armor 
protection, mobility of action is thereby reduced and the upper position still remains 
a great tactical advantage. Lanchester, of the British Advisory Committee for Aero¬ 
nautics, has evolved what he terms the N-Square Law, by which calculations on the 
probable chance of success may be reduced to mathematics. Application of the 
Ni-Square Law assumes equality in technical equipment, gunnery and individual air¬ 
manship, the fighting strength of opposing forces being then proportionate to the 
square of numerical strength multiplied by the fighting value of individual units. Two 
forces may be thus represented: 

Enemy =10 airplanes, or 10 2 100 

Friendly = 8 airplanes, or 8 2 64 

Enemy’s superiority 36 

The importance of superior tactics against the enemy is then shown by the as¬ 
sumption that the hostile formation is broken up, divided in half and attacked 
separately. The fighting value then appears: 

Friendly = 8 airplanes, or 8 2 64 

Enemy =10 airplanes, or 5 2 + 5 2 _50 
Friendly force’s superiority 14 

While application of the N-Square Law may only reflect the probability of success 
in a theoretical way, similar mathematical calculations, its creator points out, have been 
used deliberately or unconsciously by great military leaders of the past. 

While superiority in numbers in air warfare is the primary indication of success, 
the principles of aerial warfare demand an attack when there is the slightest chance of 
success, and perhaps more than in other military branches, a leader’s tactical skill is 
the deciding factor in air combat. 

WARFARE ALTITUDES 

The importance of altitude, when previously mentioned, referred to securing.the upper position when 
engaging an enemy. Flight altitudes should be considered from another viewpoint, i. e., the divisions of 
flying heights in accordance with the mission of the airplane. Set rules cannot be made on this score as 
altitude in warfare is influenced by the tactical situation and atmospheric conditions. A general classifica¬ 
tion divides flight levels into low, mean and high. Low altitude includes anything up to 5,000 feet; 
offensives against ground objective being conducted below 2,000 feet, and 2,500 to 3,000 feet being most 
favorable for night operations, bombing and photography. At mean height, 5,000 to 10,000 feet, combat 
planes have the most favorable altitude for tactical missions; photographic, fire-control and bombing 
machines may also employ these elevations. High flight, 10,000 feet and above, appears best suited for 
combat airplanes in the aircraft screen and those seeking to avoid hostile craft when proceeding on or 
returning from a mission. 

TACTICAL SKILL 

Essentially, military airplanes are fighting units, not individuals, and should operate 
in groups or formations, the strength and composition of which are governed by the 
nature of the mission. Operating singly, the duties assigned should be those which 
permit the craft to remain within areas providing support from other aircraft. 

Morale, the feeling of security and invincibility, contributes largely to success. 
Offensives successfully executed over enemy territory quickly establish the spirit of 
victory and turn possible timidity into aggressiveness. 

The particular method of attack which offers greatest probability of success is 
ordinarily pointed out by the leader’s actions. Parallel attacks head-on, from rear 
or side, give no advantage to either adversary; the importance of gaining the upper 
position has already been emphasized and is to be remembered as a fundamental tactical 
rule. When attacking with the superior force the enveloping formation is frequently 
used; circling about the enemy, the airplanes engaged thus gain concentration of fire 
and lessen the chances for escape of the quarry. Pursuit is a matter almost entirely 
dictated by the superiority of speed. Here again higher altitude offers the advantage 
of speed acceleration in descent. Once it is determined that the pursued cannot be 
overtaken before the radius of action is exhausted, or the chase continued to dangerous 
depth over hostile territory, a return should be made. The escaping plane will 
generally fly directly toward the sun or into clouds or haze; there is also a fair 
probability that when nearly overtaken its pilot will suddenly slow down and drop, in an 
endeavor to have the pursuer pass him, thus reversing the situation. 

Convoying bombing airplanes is an important duty of combat machines. Generally, the bombers 
leave the ground first, the swifter machines following some minutes later and meeting at the designated 
air rendezvous about the same time. The post of the fast fighters is above or on the flanks of the forma¬ 
tion, flying as advance, flank and rear guards. 





160 


Practical Aviation 



A successful attack on the enemy’s tail from the rear and slightly below, an effective 
method when the attacking airplane has superiority of speed 



From paintings by Lieut. Farre 

Maneuvering for position in air combat above the clouds 













Contact Patrol, Armor and Heavy Armament 


161 


CONTACT PATROL 

A tactical reconnaissance during the progress of an attack, establishing 
a liaison between infantry of the first line and their commanders in the rear, 
giving positions of friendly and enemy troops, and carrying out offensive 
actions against enemy troops on the ground—that is contact patrol, perhaps 
the most thrilling task that comes to the aviator in line of duty. 

Airplanes assigned to contact patrol duty arrive over the front line trenches 
exactly at the time when the attack is scheduled to commence, taking a position just 
over or under the predetermined trajectory for the artillery barrage fire. The progress 
of the attack is observed; when the infantry advances to its first objective, its position 
is signaled to the aviators by means of a shutter, lamp or flare. The position is traced 
on the pilot’s map, which is placed in a weighted message bag with any necessary 
comment; he flies then to the infantry headquarters, and coming down within 200 feet 
of the ground drops the bag. Sometimes the airplane’s message is delivered in tele¬ 
graph code by lamp, Klaxon horn or Very’s lights and smoke bombs; wireless is 
occasionally used, but offers the possibility of interception by the enemy and is less 
desirable. The reports preferably include the state of enemy trenches during the 
attack, troop movements and location of any new trenches. 

The offensive action, which is part of the object of a contact patrol, is literally a 
trench raid conducted in formation by combat aircraft. The usual method is for the 
first man to fly along the line of the enemy’s first-line trench, very low under the 
barrage, in fact usually less than 100 feet above the trench parapet. The second man 
takes the second, or support line, both directing downward a stream of infilade fire 
from machine guns. It is the object of the second man to prevent effective fire at the 
first-line man; the airplanes in consequence fly almost abreast. Meanwhile, the support, 
or third line trench has been covered by a third airplane, with the object of demoraliz¬ 
ing the troops in its shelter. A fourth airplane is meanwhile zig-zagging over the 
trenches, combating any attempts to direct effective rear fire from the trenches after 
the machines have passed. 

The speed of flight of all four machines is 120 miles an hour or better, eliminating 
the possibility of accurate aiming by gunners returning small-arms fire from the 
trenches. Anti-aircraft guns are also 'ineffective at the low angle. The density of the 
air at the ground and the powerful types of airplanes used make the effect of wind 
puffs or disturbances from shell bursts negligible on control. The low altitude and 
high speed also tends to make the airplane rise; to overcome this the nose is pointed 
slightly downward, pointing the rigid gun at the best angle to rake the trenches. 

When the machine guns have been discharged a return to friendly lines is made, 
a dangerous proceeding, as it requires flying up through the barrage fire, the smoke 
from which screens the craft from friendly gunners. 


ARMOR FOR AIRPLANES 

Armor, mounted in sheets protecting the airplane’s vital parts, or in the form of turrets and shields, 
proof against small-arms fire, is indispensable and practical for low altitude operations. Armor plate Ys 
inch in thickness weighs about 10 pounds to the square foot, making the weight consideration an important 
one The protection, therefore, is generally limited to armor plate beneath the motor and cockpit, dis¬ 
position and quantity being governed by the type of airplane and the height at which it is usually flown. 
Protection from overhead fire not being considered, adequate security from rifle and machine gun fire on 
vital portions is thus gained by an average armored area of 30 square feet, or by an additional weight of 
300 pounds Flying efficiency being lessened by weight additions, the heavy armor protection which 
would be effectual against artillery fire is eliminated from calculations, leaving the evasion of fire to the 
airplane’s high speed and maneuvering ability. 

Turrets and shields are furnished for protection in combat with hostile airplanes, shields being 
mounted on universal joints so they can be lowered for underneath protection when not required by 
the gunner. 


HEAVY AIRPLANE ARMAMENT 

Explosive shells to be fired from airplanes have been successfully adapted to a specially designed, 
light weight 3-inch rapid fire gun. By reason of the short ranges used, high muzzle velocity is not 
required in air combat and the great weight of the same calibered field artillery piece may be cut down 
bv elimination of the long barrel, recoil mechanism and heavy carriage. These aerial guns in consequence 
weiuh less than 250 pounds. Instead of employing hydraulic cylinders for the recoil the aviation arm 
takes up firing stresses by balanced fire, the gun having divided barrels the projectile being loaded in the 
forward barrel, the powder charge placed in a chamber between it and a second barrel which is loaded 
with fine shot. When the gun is fired the fine shot is discharged backward, its force balancing in large 
measure that of the projectile discharging in the opposite direction. The slight difference in force is the 
recoil. Wooden breechblocks which blow out rearward are also used. 

Heavy aircraft armament is used on airplanes of the super-plane class where lifting capacities of 4 
tons are usual. The 3-inch and 2-pounder airplane guns do not have the high accuracy of fire which is 
essential to field artillery pieces and given by their higher firing velocities. Accuracy and high striking 
velocity is of less importance against aircraft, for the reason that high explosives can cause the collapse 
of an airplane without actual contact with it. 


I 






Practical Aviation 


162 



British Official Photo 


Crew of an anti-aircraft battery securing ranging data 

ANTI-AIRCRAFT FIRE 

The most common trap which the aviator falls into is in diving to low altitudes 
over hostile territory and coming within range of anti-aircraft batteries. These dives 
may be occasioned by following an enemy airplane downward in heat of combat, or 
seeking to escape from a larger hostile air force. Deliberate luring of airplanes to 
altitudes within range of anti-aircraft fire is also a regular practice in warfare. Attacks 
on balloons and bombing expeditions on enemy bases also subject the military flier to 
this defensive fire from the ground. An understanding of anti-aircraft guns is valuable. 
ACTION UNDER FIRE 

The aviator under attack observes the effect of range fire directed at him by the 
white smoke of the shell bursts, termed “cream puffs.” When the sound of the burst 
can be heard above the noise from his airplane motor it may be accepted that the 
gunners are getting the range with dangerous accuracy. An escape is then in order. 
If diving or climbing is attempted the gunner may lower or raise his fire and estimate 
the airplane’s velocity with fair accuracy. Perhaps the best method of escape is to 
employ the pancake, throttling the motor and dropping several hundred feet; this 
maneuver is difficult of detection from the ground, as the machine remains horizontal 
to its original position. Zig-zag flight ahead at high speed is then usually employed, 
although the straight course is a valuable variation because of its unexpectedness. 
All forms of aerobatics are frequently used when the shells are dangerously close. 

Anti-aircraft artillery loses its accuracy of aim when the airplane is at elevations 
greater than 9,000 feet, although a chance hit may be expected. Shrapnel is less dan¬ 
gerous than high explosive shelling as a hit from its scattered fire must strike a vital 
part to be effective; explosive shells do not necessarily have to reach the target, how¬ 
ever, as the light structure of a wing may be crushed by detonation in a near vicinity. 
The principal object of anti-aircraft fire is to force the airplane to greater altitudes, 
and while the percentage of hits is relatively small, the guns are sometimes amazingly 
effective at low elevations and the aviator’s safety lies in climbing out of range. 
LOCATION AND TYPES OF GUNS 

Both fixed and mobile anti-aircraft artillery is well concealed by pits and camouflage 
from hostile airmen. The guns are of two types; important positions are usually 
defended by high power guns on fixed emplacements of concrete; the principal, and 
largest class, comprise light rapid-fire pieces, 1, \ l / 2 or 2-pounders, and heavier types 
up to 6-pounders, mounted on motor trucks of a special type. The heavy guns are 
generally used at headquarters of commanding generals of army corps, the lighter 
types being assigned to brigades and divisions in the field. While highly mobile, the 
guns are usually placed at supporting distance, about 1,000 yards apart. They have 
high muzzle velocity and consequent long range, firing projectiles with combination 
percussion and time fuses, explosive and incendiary charges. Automatic sights are 
used with graduated altitude, drift and deflection scales designed for high angle fire, 
45 to 75 degrees. Fire correction is obtained by use of special projectiles giving off 
varying densities of smoke. 





Pointers on Anti-Aircraft Fire 


163 



Mobile anti-aircraft guns mounted on motor trucks 


SHELL TRAJECTORIES AND BALLISTICS 

The trajectory, or path described by a projectile, is influenced by gravity and time or 
resistance of the air. In anti-aircraft firing the line of sight is at angles up to 90 degrees 
and seldom less than 15 degrees, consequently the trajectory is unsteady and can only be 
aided in comparatively small degree by high velocity. Velocity losses as high altitudes 
are reached also serve to magnify small errors in aiming, which in turn are liable to 
frequent occurrence because of the short time allowed for computations. 

A further contribution to inaccuracy is found in the changes in air density as altitude 
increases, affecting the ballistics of the shell. Time fuses for this reason burn erratically, 
wide variations in rate making them, unsatisfactory; the frail nature of the airplane miti¬ 
gates against the operation of percussion fuses also, even though the projectile pass directly 
through the target. The percussion type does not explode unless it reaches its target and 
is therefore valueless for furnishing firing data. 

Firing by salvo is considered the best method, four guns being arranged in a square 
at 200-foot intervals with the observer in the center. They are all aimed with the sante 
firing data, a bracket being thus obtained on which corrections are based. 

DEFENDING POSITIONS 

Aviators must not underestimate the danger from anti-aircraft fire; improvements 
are constantly being made and the exercise of proper caution is required, particularly 
in raiding defended positions. 

Outpost detector stations may be expected, equipped with microphones and other forms 
of electrical sound amplifiers which detect the approach of hostile aircraft at considerable 
distances. Telescopes and long range glasses sweep the skies constantly and powerful 
searchlights, fixed and mobile, are ready at night to throw a revealing beam on the invader. 
The outpost stations are also equipped with anti-aircraft batteries and combat airplanes 
which take to the eir at the first warning of an enemy approach. 

The line of interior defense ordinarily extends in a circle of four-gun groups placed 
at 1,000-yard intervals on a diameter of five or more miles from the defended position. 
These defenses must be passed before the objective is reached, when a fierce fire and 
engagement by combat craft may also be expected. 

ATTACKS ON BALIOONS 

Captive balloons used for observation and regulating artillery fire are most dangerous to attack. 
These helpless-appearing gas bags are about 200 feet long by 30 feet diameter, placed about 2 miles apart 
at an altitude of 4,000 feet. They are protected by several fast combat airplanes which circle above them, 
and an attack means flying through a heavy anti-aircraft barrage as well. Amazing accuracy is often 
attained by anti-aircraft gunners at the 4,000-foot altitude and the best are assigned to balloon protection. 

One of the most successful methods of attack is for the hostile airplane to fly beyond the balloon’s 
position at a minimum altitude of 6,000 feet, circling back over it and diving with the motor cut off, so 
it cannot be heard. The dive for 1,500 feet should be steep with the machine in almost vertical position 
then slightly lessening the angle so a raking fire may be delivered when within 200 feet. If the tracer 
bullets show the mark has been reached, the attacker should swerve in a wide arc to avoid the effects 
of the explosion. After delivering gun fire quick climb is usually required to avoid the pursuing airplane 
guards and the shelling from the ground. 







164 


Practical Aviation 



A bombing attack on an enemy base executed by a squadron of raiding airplanes 











Bombing Crews, Planes and Training Courses 


165 


BOMBING AIR RAIDS 

Destruction of enemy bases and headquarters, factories, warehouses and 
magazines, railroads and bridges, is the duty of specially trained bombers. 
The bombing arm of the air service, once a matter of a few volunteers operat¬ 
ing independently, has now assumed the proportion of about one-quarter of 
the total air force, operating in squadrons of 12 airplanes each. Large groups, 
consisting of several squadrons, generally conduct bombing raids, escorted 
over the lines by fast fighting squadrons, which do not continue to the 
objective owing to limited fuel capacity. Numerical increase in airplanes 
for bombing is based upon the division of defensive fire thus required of 
anti-aircraft batteries. 

TYPES OF BOMBING AIRPLANES 

Examination of the various airplanes employed for bombing reveals wide diversity in 
type, but selection according to long cruising radius and weight-carrying capacity. In 
triplane construction, machines with 3 motors, 2 tractor and 1 pusher propellers are of two 
types, large and small, the greater having a bomb carrying capacity up to 5 tons. A small 
single-seater triplane is occasionally used. In biplane types, motor power up to 600 h.p. 
is found, with 100-foot wing spreads, 2 or 3 motors and one or more guns. The single 
motor, two-seater, is also used. There are day machines and night machines in the aerial 
bombing arm, the characteristics of the night airplanes showing moderate speed and slow 
climb, but great inherent stability. 

Night air fighting is almost unknown, so speed and maneuvering ability are secondary 
to capacity for carrying explosives. 

MUFFLERS AND FLARES 

Since the objectives of bombing squadrons are almost without exception fortified 
positions, the anti-aircraft batteries are the principal sources of danger. In daylight 
raids, the enemy combat airplanes are a material menace, but their effectiveness is large¬ 
ly reduced in the dark or in the uncertain glare of searchlights. Silencing the noise of 
airplane engines by elimination of the exhaust sounds which enemy microphones detect 
miles away, requires added weight and loss of power, as against the lesser weight of 
additional fuel required for higher altitude flight. 

For night air operations parachute flares are used. These are dropped from the air¬ 
planes and light up a circular area lj /2 miles in diameter with 400.000 candle power 
illumination. Buildings, gun emplacements, railroads, wagon trains, troops or ammuni¬ 
tion dumps are thus clearly revealed and the particular target easily selected. Suspended 
by the parachute at a height of 1,500 to 2,000 feet, these flares also materially interfere 
with careful aiming of anti-aircraft guns, since the attacking airplanes are in the darkened 
area well above the light from the flares. 

TRAINING BOMBING CREWS 

Training a bombing crew, i. e., a pilot and a bomber, consists of highly specialized 
instruction in flying, navigation, fighting, aiming and firing. The men are selected 
from those of highest standing in the ground school classes. 

The preparatory stage of instruction brings the bombers together with pilots, who 
have mastered acrobatic, cross-country and formation flying. A week is devoted to study 
of the theory of bombing, explosives and sighting devices. Flights are then taken over 
courses marked by camera obscuras and Batchelor mirrors located on housetops, instru¬ 
ments by which the course of the airplanes flying over them can be traced on charts with 
the slightest errors of the crew shown. Instructors correct these errors and shift the 
crews around until the best combinations in pairing are secured. 

Bomb-dropping is the next stage of the training A. painted circle with a 25-foot 
radius is the target, the bomb being a plaster-of-Paris missile, accurately balanced and 
weighted. Low altitude flight is followed by target practice at 3,000 and 4.000 feet until 
an average score of seven hits out of ten bombs dropped is recorded. The training is then 
continued at elevations between 6,000 and 12,000 feet. The size of the target is not changed 
even when the flight elevation is two miles above the earth, at which height the painted 
disc looks like a flyspeck. Moving targets are also used, these taking the form of dummy 
trains and individual objects. 

The final stage in bombing training includes photographing of assumed enemy objec¬ 
tives and night raiding. Aerial gunnery, with fixed and movable machine guns, is also 
thoroughly mastered 






166 


Practical Aviation 



Large high explosive bomb 
used by super-planes 


Direction or mot/on 


With oirp/one 
dgo/nst head w/ncf 
Against constant headwind 
Ago/nst headwind A' 

With wind at A .... 
Without wind 
With wind... 


Rubbereue 
p/ece 


Chrcnogroph 


Movob/e pointer 
for d/sh 



Dial- 


Universal 

joint 


Movob/e 
prism, 



Pr/sm pivot 


.Dish operating 
i prism 


Control rod 
' for prism 



Figure 136 —Effect of air resistance and gravity Figure 137 —A type of telescopic 
on bomb trajectories range tinder 

BOMB DROPPING 

A bomb released from an airplane describes a curved path in its fall; this flight path, or trajectory, 
must be determined and practically applied if accuracy is to be attained. Velocity of the airplane and 

its height from the ground determine how far in advance of the target the bomb must be released, for 

the distance the missile will carry increases with the airplane’s velocity and height increases. 

The bomb is subjected to air resistance and gravity forces; if it were dropped from a stationary point 

in a vacuum its trajectory would be vertical as the dotted line in Figure 136. Dropped from an airplane 

in motion, however, it is given an initial speed equal to, and in the same direction as the motion. In its 
fall it is ordinarily subjected to the force of wind in motion. The various flight paths shown in Figure '136 
illustrate the wind’s effect on the fall with the airplane stationary or in motion. Trajectories A-B and A-I) 
are with the wind and the airplane in motion, A-C with no wind, but airplane moving, A-D, A-D' and A-E, 
with the machine flying against the wind; path A-F shows a head wind’s action on a bomb released from 
aircraft theoretically without motion. 

It is immediately evident, then, that knowledge of the velocities of airplane and wind are required. 
Best results in bomb dropping are obtained by releasing the projectile into, or against, the wind, and 
the wind velocity is easily determined by calculating the difference between the normal velocity of the 
airplane and its velocity with respect to the earth at the given time. Thus if an airplane having a normal 
speed of 90 m.p.h. is found to be flying only 70 m.p.h. with reference to the earth, then the resistance of 
the head wind is 90—70 = 20 m.p.h. It then appears only necessary to know the airplane’s altitude and 
the initial velocity of the bomb to determine the trajectory. 

Mathematical calculations are only estimates, however, due to the fact that they are based on the 
supposition that the wind is a constant force at all altitudes between the airplane and the ground, 
whereas it is well known that wind velocity varies at different altitudes and changes direction appreci¬ 
ably by veering. So while it appears comparatively easy to construct a table of velocities and alti¬ 
tudes to give the exact instant when a bomb should be released to hit the target, the ideal range finder 
awaits the day when the laws governing the capricious action of winds are fully understood. 

RANGE FINDERS 

Instruments with telescopic sights have appeared in several forms in military aviation. Probably the 
best type is illustrated in Figure 137. The telescope remains vertical, but the prism mounted in the base 
is controlled by a graduated disk. There are two indexes on the disk, one of which corresponds to the 
vertical speed, or dead point of the range finder, and the other to the vision of 22° 30'. Another index, 
fixed to the body of the range finder, serves as a basis. At 0° the marksman views the ground along the 
vertical (B in Figure 137); at 22° 30' the inclination of the visual ray is that angle (C) in front of the 
airplane; at 5° the inclination is as A, or 5° behind the airplane. A small movable index is attached to 
the disk, but is fixed by a small stop. Therefore, when the index, fixed on a graduation of the disk, 
passes the dead point it falls into a small notch, thus informing the marksman that he is viewing the 
ground according to the inclination which he had marked. 

There is a spirit level in the body of the telescope so arranged that the edges of the air bubble are 
refracted as a black circle, serving as a sighting center. While range finding, this bubble must be kept 
in the center of the eye piece so the telescope remains vertical with the ground, irrespective of the air¬ 
plane’s angle of inclination. 

A universal joint permits the free inclination of the range finder, but when the visual ray is accidentally 
directed to right or left, instead of front or rear of the route, an electric route corrector, acting upon a 
very sensitive galvanometer, indicates the necessary correction to regain the route. 





































Bomb Dropping and Range Finding 


167 





SUAP£0 PADtATOP 

RA/rfiPf/te 

ro ***><■ 
£ \ C **4**P I7£ f v 


Ofe Vs,. '.1 


U. & U. Photo. 

Drawing of a German airplane showing bomb dropping mechanism 

OPERATION OF THE RANGE FINDER—Height is obtained by subtracting the height of the 
objective from the altitude indicated by the altimeter. Thus, if the airplane is flying at 5,000 feet and 
seeks to bombard a 100 foot building the height will be 5,000—100 = 4,900 feet. 

A few minutes before arriving over the bombardment objective the two elements are found which are 
necessary to read on the chart the proper firing angle. The index on the graduated disk is set at 22° 30'. 
The range of some point forward on the ground, such as a house or edge of a wood, is found. This point 
is caught in the circle formed by the spirit level’s air bubble and followed while turning the disk until 
the index falls into the notch at the dead point; at this instant the chronograph is released and the point 
is followed in the range finder until 0° of the disk checks with the dead point, when the chronograph is 
instantly stopped. The resultant number of seconds of time given, when found on the chart in the line of 
altitude indicates the airplane’s speed with reference to the ground and the proper sighting angle in degrees. 
The index is immediately set at this angle and the bomber is ready to operate. The range finder is trained 
on the target when within a mile or two of it, and at the instant when the index fixed at the proper 
number of degrees falls into the dead point, the bombs are released. 
















108 


Practical Aviation 


Inflammable 
rope trapping 

\ 



Revolving vane. 


Stabilizing fin 


- Ignition Device 
■Thermite 


SVW 


Me/teo wh/te 
phosphorous 


Meta/cup 


Shell 


Detonofor 

'socket 

.Setxrew 



Parachute 

cords 


Locking 

spindle 


Fdeose kver x 
Sliding rod 



Stabilizing fin 

firing pin 
Percussion cap 


, head piece 

Friction 


■fxp/osive charge 

.'firing charge 

Percussion 
hammer 

-firing cops 
>-Safety sp/nd/e 
3a// bearing 
fyP/ug 


. Firing chorge 

fxp/osive 
: 'Mr-'charge 


..-Pilot 


V Point of pilot rod 


f-De/onator head 

Figs. 139, 140, 141 —Three types of explosive bombs 


Fig. 138 —Incendiary bomb 

TYPES OF BOMBS , . . . . 

Bombs for use against hostile forces may be roughly classed as (a) explosive, 
(b) incendiary. There are also smoke bombs for signaling and for smoke screens, 
rockets for attacking balloons, flare rockets for illuminating positions and steel darts 
for use against enemy personnel. Incendiary and explosive bombs will be briefly 
described. 

INCENDIARY BOMBS 


The bomb illustrated in part section in Figure 138 is of the type used for setting 
afire towns and military depots. Its metal base diameter is about 10 inches. From this 
cup base a hollow metal funnel runs through the center to the handle; this is filled with 
thermite, a composition of finely divided aluminum and a metallic oxid, which on 
ignition produces heat so intense as to melt steel. A great flare of light is thrown off 
by the thermite, its heat quickly melting the funnel; the molten metal spreads rapidly 
as the bomb strikes and sets up at once a fierce fire if it strikes any combustible material. 

Another form of incendiary bomb contains a gasoline tank mounted on an arrow shaft which, when 
the arrow point strikes, sets in motion a wheel which rotates against a ferro-cerium brush, the friction 
generating a stream of sparks which ignites the gasoline. A powder charge is also exploded, which increases 
the rate of burning. Fins maintain steadiness in flight and barbs are attached for arresting the arrow’s 
flight when used against airships. 


SAFETY DEVICES 

Airplane bombs have three safety devices; safety pin, wind wheel, and fuse device, usually a com¬ 
pression spring or resistance split ring. Safety pins are pulled before the bombs are released; wind 
wheels or revolving vanes usually act in less than 100 feet, preparing the firing pin for action on impact. 

EXPLOSIVE BOMBS 

In the illustrations above three types of aircraft bombs carrying explosive charges 
are clearly pictured in section. The action of their safety devices and firing mechanism 
will be described. 

Figure 139—The safety device is operated by the centrifugal forces during the fall, the revolving 
vane giving the bomb a rotary motion. The firing charge and detonator, placed in the nose of the bomb, 
are held separate from the firing pin by means of two spring-loaded masses. With increase in centrifugal 
force to a predetermined point the force of the springs is overcome and the firing charge is free, excepting 
for two clamps which hold it in place. On impact with the ground these give away and the charge is 
driven into the firing pin. 

Figure 140—This is a somewhat similar type of bomb with a firing mechanism also actuated by direct 
impact. Friction firing caps ignite the fuse. This illustration shows in' detail how the spring is held in 
check by the safety spindle, or pin, having ball bearings for easy removal before the bomb is released. 

Figure 141—The pilot rod in this type of bomb rests in a guide which keeps it from sliding until 
it is unlocked. Thus the firing charge is kept apart from the explosive charge, minimizing the danger from 
accidental discharge. Stabilizing fins are mounted on the tail piece. 

The horizontal suspension of the bomb from the airplane is shown in the upper view. The release 
lever automatically removes the safety lock and as the bomb gradually assumes the vertical position the 
pilot rod slides forward, carrying the firing charge into the center of the explosive charge. The firing pin 
then slides into position and when the nose of the bomb strikes the ground the pilot rod is driven back 
in its guide, bringing the firing charge in contact with the pin and percussion cap. The explosion follows. 
To make certain the sliding forward of the pilot rod the fall of the bomb is retarded by a parachute. 
Telescopic tubes are substituted for the pilot rod in some models of this bomb, opening to their fuli 
length under the speed of the fall. 

BOMB CARRIERS AND LAUNCHING CRADLES 

Clusters, or racks, are used to carry bombs, ordinarily consisting of six or more bombs. The usual 
launching cradle is composed of two sets of metal fingers, hinged at the top and pinned at the bottom. 

STEEL DARTS 

# Pointed steel spindles with spiralled tails to give a rotary motion and steadiness in flight are used 
against massed troops. From 150 to 200 are released at a time. They are non-explosive. 




















































Practical Aviation 


169 


REVIEW QUIZ 

Aerial Gunnery and Combat—Bombs and Bombing 

1. Give the essential differences between patrolling and sentinel duty 

for combat airplanes. 

2. What effect has technical superiority of airplane and armament? 

Compare pusher and tractor types for points of combat su¬ 
periority. 

3. Explain why knowledge of the appearance of enemy types of air¬ 

plane is valuable, how clouds and sun are valued in attack, 
why knowledge of aerobacy is essential. 

4. Describe the operation of the Lewis machine gun in detail; begin¬ 

ning with loading, state the successive operation of the mechan¬ 
ism; explain how the magazine feeds, the ejector operates and 
how power is developed by the cartridges for successive cycles 
of operation. 

5. Under what conditions of equality of equipment may gunnery skill 

become the deciding factor in combat? 

6. Why is high rate of fire essential to an airplane arm? 

7. Describe five common types of bullets used in aerial warfare and 

give the function of each. 

8. Compare the relative advantages of mounting machine guns rigidly 

on the upper plane and placing them to fire through the pro¬ 
peller. How is the latter accomplished? 

9. By several illustrations of machine gun arrangement show how 

effective angle of fire may be increased. 

10. There are ten principles by which skill in attack may be acquired. 

State them. 

11. What is the best method of escape for a single machine attacked 

by a hostile formation? 

12. Explain how captive observation balloons are protected and describe 

a method of attack. 

13. State two reasons why the V-shaped arrangement is preferred for 

flying in formation. 

14. Explain how a turn to the left is executed; describe how the leader 

signals attention and approach of hostile aircraft. 

15. Show by a mathematical calculation under the N-Square Law how 

superior tactics may cause the defeat of a numerically superior 
force. 

16. Classify flying heights into low, mean and high levels, and state 

how these apply to the various missions of aircraft. 

17. What is contact patrol and how does it differ from combat air 

patrols? 

18. When under fire from anti-aircraft batteries what indicates that 

the gunners are getting the range? How is escape best effected? 

19. What forces tend to destroy the accuracy of fall of a bomb dropped 

from an airplane? 

20. Describe a type of incendiary bomb, an explosive bomb and a safety 

device. 






170 


Practical Aviation 


CHAPTER ANALYSIS 

Reconnaissance and Fire Spotting 

RECONNAISSANCE BY AIRPLANE: 

(a) Orders for Reconnaissance Flights. 

(b) Preparations. 

(c) Gathering Information. 

(dj Tactical Reconnaissance. 

(e) Estimates of Enemy Strength. 

(f) Strategical Reconnaissance. 

(g) Preparatory Reconnaissance. 

(h) Reports of Flights. 

INSTRUCTION IN CODE TELEGRAPHING: 

(a) The Code. 

(b) Memorizing the Code. 

(c) Proper Grip on the Key. 

(d) Sending. 

(e) Receiving. 

(f) Visual Signaling. 

(g) Proficiency Required. 

DIRECTING ARTILLERY FIRE: 

(a) General Considerations. 

(b) Types of Shells. 

(c) Ranging. 

(d) Observer’s Map and Code Signals. 

(e) Signals from the Ground. 

(f) Method of Training. 

RADIO (WIRELESS) TELEGRAPHY: 

(a) Theory of Radio Transmission. 

(b) Operations in the Circuits. 

(c) Radio Receivers. 

AIRPLANE RADIO APPARATUS: 

(a) Generating the Electrical Power. 

(b) Regulating the Power Output. 

(c) Transforming the Energy. 

(d) Controlling the Length of the Radiated Wave. 

AERIAL PHOTOGRAPHY: 

(a) The Camera and Its Parts. 

(b) Arrangement of Cameras. 

(c) Photographic Flights. 

(d) Mapping from Photographs. 



t 


CHAPTER XV 


4 


► 


Reconnaissance and Fire Spotting 

Reconnaissance, the military term for the duty of gathering information 
in the field, represents a large share of the duties assigned to the service of 
aircraft. In fact, the utility of the airplane for this work may be said to 
represent its chief value in Warfare. Offensives in the air are mainly defen¬ 
sive measures to prevent enemy reconnaissance, and raiding by bombing 
and in co-operation with land forces in attack, are subsidiary in importance. 
By and large, the air forces are, and will remain, scouts and informers for 
commanding officers of troops engaged in land warfare. 

All military aviators are charged with reconnaissance; no matter what 
their duties may be, while in flight they are required to collect all obtainable 
information of military value. 

Aerial reconnaissance presents features which are primarily for specialists, 
for gathering information of strategical and tactical value is accomplished 
by devices and methods mastered only by careful study. Artillery control, 
or lire spotting, is also not a task for the novice, and specially trained men 
are required. These soldiers of the air are known as observers, and in 
addition to textbook and class-room study courses, they undergo special 
training under flight conditions. The latter course begins with visibility 
tests in clear weather by naked eye, use of field glasses and identification of 
known objectives and their comparative sizes from successive heights of 
1,500, 2,000 and 3,000 feet. These observations are then repeated in unfavor¬ 
able atmosphere, flying in, below and above broken cloud formations. The 
altitude is then increased to 5,000 feet; buildings and structures at a given 
point are sketched on an incomplete map. All roads, trails, bridges and 
docks within a given area must then be recorded on the map, the tests being 
repeated at flight altitudes of 6,000 and 8,000 feet. Higher altitudes, 9,000 
and 10,000 feet are then sought. Photographic flights are made, flight orders 
and reports are prepared and a military reconnaissance made over an ex¬ 
tended area. Signaling to and from the ground is then practiced and control 
of artillery fire mastered. The flying course ends with tests showing ability 
to use the machine gun effectively at targets while in flight. When the 
observer has completed the course he is able to identify and give the pro¬ 
portions of the following objects: buildings, roads, bridges, wharves and 
docks, airdromes, aircraft on the ground, trenches, troops, motor cars, wagons 
and artillery, gun emplacements, mine fields and shell bursts by color and 
by patterns. 

Aside from manipulation of radio (wireless) apparatus, the observer must also 
acquire proficiency in sending and receiving visual signals, made by lantern, helio¬ 
graph, searchlight, rockets and the Very pistol, all communicated by dot and dash 
code. Great technical skill with apparatus and high speed communication is not 
required, but the diversity of subjects requires the observer to be of a good order 
of intelligence with highly developed powers of concentration. 

171 


172 


Practical Aviation 


RECONNAISSANCE BY AIRPLANE 

Reconnaissance by airplane has three distinct classifications: (a) tactical, or the 
gathering of detailed military information in a limited area while troops are engaged 
in combat; (b) strategical, or securing of information and general military impressions 
over an extended theatre of operations; (c) observations for control of artillery nre. 
The last is actually a separate duty, but is so closely related to reconnaissance that it 
is best included under that bread head. 

ORDERS FOR RECONNAISSANCE FLIGHTS , , , 

Orders for a flight may originate with the headquarters staff or the squadron commander, and are 
preferably written. They contain the serial tactical number of the flight; the airplanes, pilots and 
observers to participate; the time, place and route, and the mission to be performed. How, when 
where the report is to be delivered and its nature, is stated. Ordinarily, the orders are issued sulhciently 
early so pilot and observer may make a preliminary study of the situation. 

PREPARATIONS 

Pilot and observer, generally a pair accustomed to working together, immediately 
on receipt of orders consult together as to the best manner of fulfilling the mission. 
Route calculations are made from the map, the pilot makes a test and final inspection 
of his machine and the observer insures that signaling apparatus, note paper, pencils, 
weighted message bag, field glass, watch, camera and all necessary aids are included 
in his equipment. The speaking tube, or aviaphone, for their intercommunication is 
made ready, and a simple code of signals arranged. 

GATHERING INFORMATION 

The observer’s logical position in the airplane is the front one, enabling the pilot 
to easily watch his signals. When the stated objective, or a position showing activity 
of military interest, is reached, the pilot manipulates his controls so the best possible 
view is afforded the observer. Figure 8s, steep spirals and banking are employed, so 
the observer may make a prolonged observation with vision unobstructed by wings, 
struts or other parts of the machine. The observer is charged with the gathering of 
facts; opinions and deductions may be made, but they are always reported as such. 
Once the necessary data are gathered it is the concern of both pilot and observer to 
bring back the information safely, high altitudes being sought and combat avoided by 
flight. Hostile aircraft is engaged only when absolutely necessary. 

PREPARATORY RECONNAISSANCE 

Preparatory reconnaissance duty, as the term implies, is conducted at the outbreak 
of hostilities; it is strategical and offensive in character. The objects are to secure all 
data in connection with the enemy’s mobilization, to locate depots and munition bases 
and plants, to harass and destroy hostile forces by air raids, interrupt transportation 
and break lines of communication; and, up to the point of concentration and establish¬ 
ment of a theatre of operations, to locate all hostile forces and determine their strength 
and mobility. 

TACTICAL RECONNAISSANCE 

Observations to be made on a flight order for a tactical reconnaissance are limited 
to the immediate area in which hostile forces are in contact. A two-seater airplane 
with radio and photographic equipment is generally used, and the report comprises 
detail sketches, the positions of troops and fortified terrain. Reports comprise the 
following information: 

Troops—Positions, and strength of reserve; movements, enveloping or turning, infantry and cavalry. 

Artillery—Positions and number of guns. 

Field Trains—Positions and movements of combat and field trains behind intrenched positions. 

General—Evidences of strengthening or weakening fortified lines; activities indicating attack in force 
or retreat. 

Tactical reconnaissance in general has two purposes and may therefore be divided 
into (a) battle, (b) protective. 

Battle—Supplying detailed information of all changes and developments during 
the course of action by which the commanding general may estimate the situation and 
form decisions. The following information is required: Location of existing and 
changing trench lines and batteries; changes in tactical disposition and distribution 
of combat troops; arrival and departure of supporting troops; changes in location of 
depots, field bases and lines of communication; concealment of new and old positions: 
movements of artillery, new positions, number and calibers of guns; movements of 
transport and combat wagons and trains. 

Protective— Information similar to the above, but relating both to enemy and 
friendly forces, is secured in detail during a retreat of friendly forces. The command¬ 
ing general by this means is enabled to keep his troops under full control and estimate 
the probable moves of his adversary. 

The value of both types of tactical reconnaissance lies principally in the continuity 
of the reports. Airplanes engaged in this work make brief but regular and frequent 
observations, working in relays if necessary. From captive balloons, in rear of the 
actual contact of forces, supplementary and continuous observation is made. 




Strategical and Tactical Reconnaissance 


173 


ESTIMATES OF ENEMY STRENGTH 

Moving Columns -Quick computation of the approximate strength of columns 
moving along a road will be facilitated by the following rough calculations: 

fa ntry in column of squads occupies a depth of about yard per man, a column 
1 mile long contains about 3,500 men. 

Cavalry in column of fours, about 1 yard per horse, a column 1 mile long containing 
about 1,500 troops. 

Artillery in single file, requires about 20 yards per gun or caisson, field artillery 
having about 50 guns to the mile. 

Estimates of strength may also be roughly calculated by the time taken to pass 
a selected point. In 1 minute, about 175 infantry will pass; 110 cavalry at a walk, 200 
at a trot; 5 guns or caissons. For infantry and cavalry in column of twos, take one- 
half of these figures. 

Confusion of combat troops with transport trains and artillery should be guarded 
against. Dust clouds will help the identification, if the troops are not distinguishable, 
thus: infantry dust clouds hang low; cavalry dust clouds are higher and disperse more 
quickly; artillery and wagons raise dust to unequal heights and of disconnected form. 

Reports of marching columns should give the exact location of the troops on the 
map, the road used, direction and rate of march. Gaps in the column and unusual 
dispersions should be noted and care exercised that advance, flank and rear guards are 
not confused with the main body. All troops on foot are considered combat troops. 
Large commands are accompanied by field trains. 

Intrenched Positions—Detailed information of the field works and an estimate of strength with the 
initial deployment of troops is required. 

Trenches—By photography, sketches and notes, complete data on enemy positions are secured. The 
reconnaissance establishes: the exact line of field works, their depth including reserves, location of lines 
of communication and field headquarters. Intrenchments under construction are reported during every 
stage of development and accurately traced and located during and after erection of the camouflage 
screen. The condition of enemy barbed wire may be estimated by the ground smudges and spots, 
indicating breaks by shell fire. 

Combat Troops—Estimates of strength in the first line are figured as one man per yard. In initial 
deployments the strength of supports and reserves is of greatest importance, as two-thirds of the force of 
combat troops are usually held in the rear. 

All activities should be noted, including changes in disposition and distribution of troops, location of 
flanks and movements in the rear. 

Artillery—Battery sites should be located and all changes reported. When artillery positions are 
known estimates of gun calibers may be made by the range bursts. The usual maximum for field artillery 
is 6,500 yards; heavy artillery of medium caliber, 8,500 yards; large calibered heavy guns and howitzers 
have ranges ordinarily beyond the scope of a tactical reconnaissance. 

STRATEGICAL RECONNAISSANCE 

The object of strategic reconnaissance is to prevent surprise by the enemy. The 
term is applied to long flights over wide areas and to considerable depths of enemy 
territory, observation being made of all hostile movements and developments in the 
theatre of war. Airplane squadrons or groups with large radius of action are employed 
at all altitudes from 1,000 to 12,000 feet. Flights for information of strategic importance 
should be so frequent as to be almost constant, since upon the information thus obtained 
the commanding general must base his plans for future operations. Photography is 
extensively employed, but notes and reports are less concerned with details than with 
general impressions from which the enemy’s intentions may be calculated or deduced. 

Bases and Supply Transport activities aid in disclosing the enemy’s intentions. Railroads, roads, 
rivers, canals, harbors, depots, airdromes, lines of communication and bases should be under constant 
observation. 

Reconnaissance over wide areas is of greatest value when reports and photographs comprise the 
details given below. 

Railroads—New and old, direction, number of tracks, stations, junctions and spurs; train movements, 
size, direction, speed and frequency of travel. 

Roads—-New and old, nature, condition, intersection with railroads, extent and character of traffic. 

Bridges—Position, length and breadth, materials and construction, approaches and how screened. 

Rivers and Canals—Direction, width and depth, rapidity of current; location, size, number and 
direction of movement of vessels. Number and location of locks in canals and islands in rivers. 

Villages and Towns—Their situation and nature of the surrounding country; construction and type 
of houses, alignment and width of streets; defenses. 

Woods—Situation, extent and shape, number and extent of clearings, nature of roads through them, 
marshes or ravines within ; whether affording cover for artillery or troops. 

Marshes—Extent and means of crossing, defensive measures and possible uses. 

REPORTS OF FLIGHTS 

Reports are required at the conclusion of all flights, whether the nature of the mission is reconnais¬ 
sance, combat, bombing, or special duty. These are preferably presented on prepared forms, together with 
maps, sketches and notes. Verbal reports may be made if the need is urgent, but should later be supple¬ 
mented with a detailed written report at the earliest possible moment. 

The observer submits reconnaissance reports. Serial number, time, and similar data 
which appeared on the order for flight, is filled in; to this is added the data secured, 
arranged in chronological form, giving the exact time of each observation. Special remarks 
are added to cover air combat with the enemy and any resultant damage to the airplane. 
The course followed should be clearly stated, thus: Cambrai — Denain — Valenciennes — 
Maubeuge — Aulnoye—le Cateau — Cambrai. 


174 


Practical Aviation 



Figure 142 —The exactly correct method of gripping 


L 

*bbb •• 


B 

■ • • • 

H 

• ••• 

M 


C 

l*MH* 

I 

• • 

N 


■ • • 


V 

• ••l 


I** 


R 

• MB* 

w 


Wait 


9 

• •• 

X 

mmm • • wmm 

Understand 


the telegraph key 

E F 



Don’t Understand 

Mi* **«M* 


PeViod 


Interrogation 

•*bbh«* 


Exclamation 



3 

• ••BiBi 


7 

BiBi * ** 


0 


Call 


Finish 

• mb 


or 


Figure 


14 3—The General Service Code of the U. S. Army „ variously known as International 

Continental and Wireless Morse 



(C) Comm. Pub. Info. 


U. S. Army student aviators at a code practice table used for instruction 


















175 


Signaling Code and Method of Learning 


INSTRUCTION IN CODE TELEGRAPHING 


Military aviators are required to attain a fair proficiency in code telegraphy, requir¬ 
ing about 40 hours’ study on the average. Application of the dot and dash method of 
signaling to various forms of electrical and visual devices largely governs communica¬ 
tion in the air service and must be mastered. The following text will prove of great 
assistance in learning code if intelligently used by the student. 

THE CODE 

Although use of printed code charts which visualize the alphabet is generally for¬ 
bidden the beginner, experience has proven that, deprived of these, the novice will 
acquire them somehow, so the General Service Code of the U. S. Army is illustrated in 
Figure 143. This alphabet is variously known as International Morse, Continental 
Morse and the Wireless Code. It differs from American Morse principally in the 
elimination of the spacing between symbols making up a letter. 

MEMORIZING THE CODE 

The primary rule for success in telegraphing is that the letters must be learned 
by their sound. Under no circumstances is the student to attempt to visualize each 
letter by dots and dashes. An excellent method for those who feel the chart essential 
in the early stages is to pronounce the syllable “tub” for the initial dot, “dull” for the 
other dots, and “dah” for the dashes, the letter L, for example, being “tub dah dull dull.” 
By short periods of practice a sense of the rhythm of the letters is thus acquired. Divi¬ 
sion of the chart into progressive relationship of dots and dashes has also proved 
convenient, thus: 


e . 
i .. 
s ... 

H . . . . 




A . _ 

U . . _ 

V . . . _ 



N 

D 

B 



N 

G 

Q 

Z 


The rule governing length of symbols is: Dash is three times as long as dot. 
Space between letters equals duration of one dot. 

PROPER GRIP ON THE KEY . , , 

Figure 142 illustrates the exactly correct manner of holding the key. The positions of the fingers 
are relatively the same as for holding a pen or pencil with a diameter as large as the key knob—thumb 
against side of knob to steady it; index finger convexed or straight—never concaved—and second finger 
resting easily in position over the key knob. The wrist should be relaxed and an even, light pressure 
given the key. Tapping should be avoided. Acquiring the correct position for telegraphing is a matter 
of importance for the novice, as clearness in forming dots and dashes is largely dependent on the action 
of hand and wrist. 


Some instructors have stated it inadvisable for the student to take up key manipulation before pro¬ 
ficiency in receiving bas been acquired. Experience dictates that sending and receiving should be taught 
together for the student in early training invariably receives easiest those letters which he sends best. 

In sending, dots should be made short and sharp, but firm. The dash is made three times as long as 

the dot but not by pressure three times as hard. Spaces between letters are the duration of a dot. In 

forming letters, combination of dots and dashes should be sufficiently close in succession, so the receiver 

cannot^mistake’the combination for a somewhat similar letter. . 

Speed above 10 or 12 words per minute is not required of the military aviator, but absolute accuracy 
is insisted upon. Not only must letters and numerals be formed perfectly but spacing of groups be equally 
accurate. Concentration on typical signals from an airplane is advisable, for learning all other phases is 
lost time from the military aviator’s standpoint. Examples follow : 

YW5F7 N4SL2 AC6E9 


and so on in various S-letter arrangements including numerals. A considerable number of abbreviations 
and conventional signs are ordinarily appended to the code charts; all of these need not be memorized by 
the aviator, the following being sufficient: 

break — ... — correction. 

end of message . — . — . ch- 


The signals of radio (wireless) and buzzer, with which the airman is concerned, are exactly counter¬ 
feited by a little instrument known as a practice buzzer. Where the candidate wishes to prepare himself 
before going to tbe army schools—where these signals are received in head telephones at practice tables— 
the practice sets may be used at home, or the Marconi-Victor special set of progressive lesson records be 
listened to on a phonograph. Receiving practice is most beneficial when students are paired, alternately 
sending to each other for 15 minute periods, the faults of one thus being corrected by the other. In writing 
messages zero is distinguished from the letter O by placing a dot in its center; the figure 1 is made with 
a single unstroke so as not to be confused with I. The entire art of receiving rests on the one principle 
emphasized above-read by SOUND. 

VISUAL SIGNALING , . , , , , 

The average time devoted to an aviator’s buzzer instruction is 34 hours; 6 hours on lamp and panneau 
(signaling panel) follows, proficiency in visual code work being adequate at 4 words per minute. 

PR ^nu^n'i?^xandnation^or^aviators determines tbe ability to send and receive 5-letter words at a speed 
„f O words ‘ner minute for two successive minutes. Tf more than 6 symbols are received incorrectly, or 
more than 5 sending mistakes are made, the applicant has failed in the test. Tn sending, an interval 
omitted or misplaced is an error. 






Practical Aviation 


176 




f mm 


Com. Pub. Inf. 

The air service cadets in the gallery are simulating all the conditions of an aerial observer lookina dowt 
from a plane 6,000 feet higli l on a part of a typical earth view reproduced in the map below The instruct™ 
in the lower forefront is flashing various colored lights, representing various kinds of’artillery fire 






V 









177 


Methods Used in Fire Spotting 


DIRECTING ARTILLERY FIRE 

Regulation of artillery fire by observers in airplanes is now considered 
indispensable in warfare, aerial fire correction having practically superseded 
all other methods. Fire spotting, while distinct in many ways from the scout¬ 
ing duties of reconnaissance, is closely related to tactical operations and is 
therefore included under the broad classification. 

Since the airplane observer, by S-turn and circle, hovers over the target, a 
comparatively low-speed machine is preferred; it is generally a two-seater, 
carrying pilot and observer. Wireless, or radio telegraphy, is the principal 
means of communicating the correction for the artillery and has almost entirely 
replaced former means, such as lamps and smoke bombs. Observers for artil¬ 
lery usually work in two-hour tours, twice a day, observations being made 
at 6,000 to 7,000-foot altitudes. They are required to know something of types 
of artillery, shells and their trajectories, be able to distinguish distances and 
characters of shell bursts by the smoke puffs and, of course, understand the 
manipulation of radio transmitting apparatus. 

METHOD OF TRAINING 

The photograph on the facing page clearly shows how artillery fire spotting is 
taught. The student observers are seated in a gallery looking down on a relief painting 
which visualizes a sector of the earth as it appears at an elevation of 6,000 feet. By 
a switchboard, the instructor flashes various colored lights, representing various shell 
bursts; these blink successively at numerous points on the miniature battlefield, for 
the entire area is wired with small electric lamps. The students locate the flashes on 
their maps and record the required signals, the simulated artillery fire being varied 
in speed by the instructor’s stop watch. 

TYPES OF SHELLS 

Artillery shells are (a) common, (b) high explosive, (c) shrapnel. High 
explosive shells produce black smoke when they detonate, and greenish-white 
smoke otherwise. Shrapnel gives off a white smoke pattern, easily seen when 
the shell bursts in the air, but difficult to observe when the shell is exploded 
by contact with the ground. Both time and percussion shells are used. The 
degree of accuracy required in striking the target is greater with the high 
explosive shell, as its effect is limited to less than 10 yards, although causing 
very great damage within that area. Shrapnel, on the other hand, is most 
effective when it bursts above the ground; when time fuses are used the shells 
explode in the air about 25 to 75 yards short of the target. 

RANGING 

The observer is told before leaving the ground whether the correction to 
be made is for a single gun or an entire battery, whether the fire is to register 
positions or for destruction, and whether correction is to be given for line 
(right and left) range (over and short) and fuse (burst) or all three, and in 
what order. 

One of the principal objects of the flight is the disclosure of new enemy batteries 
and the location of screened or camouflaged positions. When the target has been 
determined and shelling begun, the result of the fire is reported by wireless by a pre¬ 
arranged code. These codes vary in detail and are changed from time to time to main¬ 
tain secrecy, but all forms require use of small divisions of the military map. 

OBSERVER’S MAP AND CODE SIGNALS 

The map of the sector which is carried by the observer corresponds exactly with 
the one to be used by the artillery. It is usually on a large scale, say, 3 inches to the 
mile. Divisions into squares are made so that smallest squares cover a very small area 
of ground, enabling corrections to be made with amazing accuracy. How the map is 
divided may be understood by careful reading of the following explanation, which con¬ 
siders the map in an initial division into squares, and three subdivisions into progres¬ 
sively smaller squares. 




178 


Practical Aviation 


Division —The map is divided into 24 equal squares, in 4 horizontal rows, 6 squares 
to a row. Each section is marked, progressively from left to right, with a letter of the 
alphabet. These letters are Capitals, A to X inclusive. 

1st Subdivision —Each of these lettered squares is subdivided into smaller squares, 
the top row (A to F) and the bottom row (6'toX) having 30 sections, or 30 small squares; 
the two inside rows (G to R inclusive) are subdivided into 36 small squares 
each. These small squares are given a number, 1 to 30 for those in the top and bottom rows, 
1 to 36 for those in the inside rows. Thus the original square A, for example, is now divided 
into 30 sections, numbered, left to right, fom 1 to 30. Squares in the inside rows, G, for 
example, are divided into 36 numbered squares, 1 to 36 inclusive. The map which was first 
divided into 24 squares (A to X) now, therefore, has a total of 792 divisions. 

2nd Subdivision —Each of these 792 small squares is divided into 4 parts, lettered 
a, b, c, d. The map consequently shows a division thus far into 3,168 small squares. 

3rd Subdivision —Each of the 3,168 lettered squares (marked a, b, c, d ,) is further 
divided into 24 equal sections, these still smaller squares being each given a number from 
1 to 24. The total division of the map is thus seen to be into 76,032 squares, each of which 
represents a very small ground area. 

The signaling is simple. A shot is fired and the point where it strikes is located on 
the map by the observer. He finds it has landed in the division A, in its lower right hand 
corner; say, square 30. This square being divided into 4 sections, he notes that the shell 
has struck in the second square b, and since the exact location of its striking point there is 
in the upper left hand corner, he notes the designation of that particular square, the 
numeral 1. He flashes by radio to the artillery, therefore, the following message: A-30-b-l. 
from this message the artillery man can locate the point where his shell struck with almost 
minute accuracy. For if the observer’s sector comprises as much as 6 square miles, he 
has given the location within a section of about 9 yards dimension. 

A high explosive shell or a shrapnel shell dropping within this distance of the 
target will have the desired destructive effect. It follows, of course, that if the area 
of the sector under observation is reduced and the scale increased, the location can be 
determined to pin-point exactness. 

Owing to the comparatively small size of the page in this book, it is not practical 
to illustrate the division of the map by a diagram, but the student may easily visualize 
the map division into squares by laying one off on a large sheet, and following the 
description. 

Another method of signaling the results of shots fired at a definite target is known 
as the clock system. By this method the point where the shell strikes is communicated 
relative to the target. Only one letter and one numeral are required. 

The dial of a clock is divided into points of the compass: 12 being north; 6 
being south; 9, west; and 3, east. The target is the center of the dial. From this center 
equally spaced circles radiate outward. These circles represent, say, 10 yard intervals; 
they are progressively lettered, A, B , C, D , etc. Thus the signal 3-C would mean that 
the shell struck 30 yards east of the target. For 3 is east on the clock dial and C being 
the letter of the third circle from the center, and each circle being spaced 10 yards 
apart, 3x10—30 yards. 

This system is susceptible of almost innumerable changes, as the relative compass 
positions merely have to be shifted to other numerals on the clock dial, and the interval 
between circles be given a different value in yards or feet. 

As more than one observer may be using the clock system at the same time in 
nearby localities, each battery has a code symbol, frequently changed, which the 
observer calls before sending his fire correction. 


SIGNALS FROM THE GROUND 


When fire is centered on a target or the objective destroyed the aviator is given 
a new position by signals from the ground. These are generally of visual character, 
although the remarkable development of radio promises wireless reception by the 
airman in the near future. 

The usual means employed for visual communication are shutter panels, lanterns 
or heliograph mirrors; by these, lettered abbreviations are signaled in telegraph code; 
or 3 white canvas strips measuring 15x3 feet are laid on the ground to form various 
characters with predetermined meanings. Thus X might mean “Commence observing 
for range”; V, “Go out”; I, “Come in”; N, “Cannot comply with last signal” or “Dis¬ 
tress”; T, “Turn”; H, “Incline to the right”; L, “To the left”; II, “Descend”; III, “Ob¬ 
serve for burst,” etc., etc. These meanings and arrangements of the 3 strips are obvi¬ 
ously easy of variation to maintain secrecy. 


Radio messages should not be sent while the airplane is turning. 
Sending with the machine pointed toward the ground station facilitates 
easy reception. 




Theory of Wireless Telegraphy 


179 


RADIO (WIRELESS) TELEGRAPHY 

Extensive knowledge of radio, or wireless telegraph sets is not required of the 
military aviator, except for those who specialize in this art, in which case full knowl¬ 
edge of theory and practice is essential.* All aviators, however, in addition to skill in 
code sending, must have some knowledge of the parts and connections of the apparatus. 
An outline of the theory of radio and a brief description of a typical airplane wireless 
set will therefore comprise the limited discussion here. 

THEORY OF RADIO TRANSMISSION 

A radio sending set comprises an assembly of electrical devices which generate 
and control an electrical wave motion, so that when the circuit is interrupted disturb¬ 
ances are created in the ether in the air, of long and short (dot and dash) duration. 
These disturbances, or waves, may be compared to the radiating ripples caused by a 
stone dropping into water, excepting that they travel in the ether with the speed of 
light, 186,000 miles per second. Reception of signals is possible only through properly 
attuned electrical apparatus; viz., the radio receiving set. Thus radio transmission 
might be further comparable to the voice, as a transmitter, sending vibrations of vary¬ 
ing intensity in waves through the air, registering only on attuned ears, the receiver. 

Easiest understanding of the apparatus which comprises a radio transmitting set is 
gained by classifying according to their functions in utilizing electrical energy, the re¬ 
spective missions being: (a) generation, (b) regulation, (c) transformation, (d) control. 

Before considering these in classification and in their relation to each other, a few electrical defin - 
tions are necessary. 

VOLT—The unit of pressure, or electromotive force. 

AMPERE—The unit of current flow, comparable to gallons of water flowing through a pipe, or 
revolutions of an engine, per second. 

KILOWATT (Kw.)—The unit giving the power required for specified work in a given time (Kw.= 
volts + amperes). 

DYNAMO—A mechanically driven machine which rotates a wire coil within a magnet, the resulting 
induced current, or electromotive force, being collected by brushes. 

DIRECT CURRENT (D.C.)—An electrical current constant in direction. 

ALTERNATING CURRENT (A.C)—A current changing rapidly back and forth from positive to 
negative direction. 

OPERATIONS IN THE CIRCUITS 

Tracing the current through its successive movements in the airplane radio trans¬ 
mitting set is made easier by classification of apparatus into four divisions by function: 

GENERATION—A small air screw, placed at the front of the airplane and rotated by the wind when 
the craft is flying, supplies the mechanical force which drives the dynamo. Direct current (D.C.) is thus 
produced. But direct current cannot be transformed to the high voltages (pressure, or electromotive 
force) necessary to transmit the radio signals through space, so alternating current (A.C.) is produced in 
a special dynamo, or alternator. 

Both D.C. and A.C. dynamos are usually contained in the same pear-shaped case, the D.C. current 
being required to excite the coils of the A.C. dynamo, or alternator. The combined apparatus is known 
as a separately excited alternator. 

Sets used on training planes often have storage batteries in place of the D.C. dynamo. 

REGULATION—A coil of wire, known as a resistance coil, or field resistance, allows the power out¬ 
put of the alternator to be varied by setting sliding contacts so as to include many or few turns of 
resistance wire. 

TRANSFORMATION—The amount of alternating current selected then goes to the transformer, 
where the low voltage is converted into high voltage A.C. 

The high voltage current then feeds to the condenser, where the electrical energy is stored up in the 
spaces between plates made of copper or some conducting material. This current discharges periodically 
(usually 1,000 times per second) through the oscillation transformer and across the spark gap. 

The oscillation transformer regulates the condenser discharges of the current to frequency desired, 
by variation of the number of turns of copper ribbon of which it is composed. 

The spark gap acts as a valve, discharging the condenser when the telegraph key is depressed, caus¬ 
ing an electrical spark to jump across the gap between its two terminals. 

When, by pressing the telegraph key, the flow of current through the circuit of the spark gap is 
interrupted, the current goes to the aerial or antenna (a wire trailing from the airplane), and part of its 
energy is radiated into space in the form of electro-magnetic waves. These electrical displacements are 
long and short according to the sequence of dashes and dots made by the key. 

CONTROL—It is obvious that without means provided for regulating the length of the r?diated 
wave, there would be conflict between a number of wireless messages hurtling through space, the dotS| 
and dashes would be confused and could not be understood. Therefore, radio sets send their signals out 
in selected, definitely measured, WAVE LENGTHS. 

The control devices used for this purpose are: the oscillation transformer, already referred to, the 
aerial tuning coils and the variometer. The aerial tuning coils, by increasing or reducing the number of 
turns of wire placed in the aerial circuit, lengthen or shorten the radiated wave. The variometer (con¬ 
sisting of two coils opposed to each other) permits a finer adjustment of wave length than the aerial coils 
alone could give. # ... 

Wave lengths are measured in meters. Placing a wave length changing switch to the desired numeral 
on a dial sets the control devices for the operator. An aerial ammeter, by its needle indicator, shows 
whether the flow of electrical energy is at maximum for the radio set’s best operating efficiency. 
RADIO RECEIVERS 

Description of the construction and operation of radio receiving sets will not be included here, as 
at present the military aviator is not concerned with their manipulation. The day is not far distant, 
however, when wireless telegraphy and telephony will take the place of visual communication to aircraft, 
and for those who wish to specialize in radio, time will be well spent in study of receiving apparatus. 
Space limitations do not permit discussion of receivers here, but excellent textbooks which go exhaus¬ 
tively into the subject, may be secured at low cost. 

* Practical Wireless Telegraphy, by Bucher, is the most suitable textbook, in the Author’s opinL.t. 








180 


Practical Aviation 



C acral Uric/1 wing Wave ity/tl Power 

tuning :c w//s Onitging snitch vifot 


ft 

Una! 


Resistance 
./ coil 


nsf 


. tana 
tmter 


erdm 


Transformer 
Condenser 


•Ccm/ecf/One 
^enercfor 


Figure 144 —View of the interior of a typical 
airplane radio transmitter 


K-i 

_ m Wove length 

'changing s». 



field resistance 


iAMftftf 

Power control : Cky ttxt 
Transformer switch \ \ 

t _ „ i pf' 


Condenser 


A ) Aerial 
Ammeter 


~r'-< Oscillation 
Transformer 


Spark p . 
gap 


i 




1 = 1 ' 



/fey 

f y 

! flags ! 

S is 

Tn/ter 







VVA'A'/ 


Figure 145 —Diagram of the circuits of the 
radio transmitting set shown above 


AIRPLANE RADIO APPARATUS 

Great advances have been made in the design of radio apparatus for airplanes, and 
sets remarkable both for mechanical and electrical perfection are now in use in war¬ 
fare. For military reasons, these cannot now be described. The aviator, being con¬ 
cerned with knowledge of fundamentals only, may acquire these from the transmitting 
set pictured in photograph and diagram on this page. It is of enemy manufacture, and 
a fair specimen of short-range radio apparatus used on military airplanes. 

The generator is not shown, as it is of the usual type, but the photograph of the set’s interior, Figure 
144, clearly identifies the various parts of the sending apparatus. The diagram of connections, Figure 145, 
is arranged for easy reference, the course of the electrical current, as given in the description following, 
being in a general direction from right to left, 

































































181 


Description of An Airplane Wireless Transmitter 


The classification scheme, outlined on page 179, is applied to the apparatus as 
follows: 

GENERATING THE ELECTRICAL POWER 

Referring to the lower right of the diagram, the exciter (a small generator) furnishes initial current 
t°'the field magnets of the D.C. dynamo; the latter in turn supplies field current required by the alternator 
(A.C.). All of these comprise the generating unit, which is mechanically driven by a small air screw, as 
explained on page 179. The current is delivered by the generator at pressures from 110 to 500 volts, 
oscillating at 150 to 500 cycles per second. 

REGULATING THE POWER OUTPUT 

Regulation of the generator’s output (110 to 500 volts) is secured by the field resistance coil (upper 
right of diagram). This generator control circuit is indicated by the broken lines. 

TRANSFORMING THE ENERGY 

The alternating current flowing from the generator (A.C.) enters the transformer (center of 
diagram) by the primary coil (P). This coil consists of a few turns of coarse wire wound about an 
iron core. The core also has a second winding of finer wire and greater number of turns, known as the 
secondary (S). The current surging through the primary (P) “steps up” the current in the secondary 
(S) to 10,000 to 15,000 volts, the electromotive force necessary for this particular type of set to transmit 
radio signals. 

This high voltage current then enters the condenser, where it is stored up temporarily, the con¬ 
denser discharging periodically (as explained on page 179) through the oscillation transformer across 
the spark gap. 

When the telegraph key is depressed, the alternating current (oscillating at high frequency) is dis¬ 
charged from the condenser across the spark gap, which suddenly quenches out the current flow in the! 
circuit, including the condenser, oscillation transformer and the spark gap. This transfers (by electro¬ 
magnetic induction) the current to the circuit, oscillation transformer-AERIAL. The energy is then 
radiated from the aerial into space as an electric wave motion. Long and short pressure on the key 
thus releases the energy in dashes and dots of the code. The aerial is a lightly weighted trailing wire 
which passes through the floor of the fuselage and is unwound to the required length from a reel operated 
by a clutch. 

CONTROLLING THE LENGTH OF THE RADIATED WAVE 

It has been explained that to avoid conflict of many wireless messages in the air at the same 
time, the electromagnetic waves are measured in definite wave lengths. The radio transmitting set 
illustrated is designed to send its message on three wave lengths, 150 meters or 200 meters or 250 
meters. This means that the operator on the ground who is to receive the aviator’s wireless message 
will attune his set to one of these waves, selected according to the interference prevailing and the dis¬ 
tance to be spanned. 

Adjusting the various parts of the apparatus so the radiated wave will have the desired length is 
accomplished by setting knobs and switches on the top of the transmitter case. It is the principal 
adjustment required of the operator, and the resultant action in the circuits is the most difficult for 
the student to understand. 

First it must be known that the length of the wave radiated from the aerial has direct relation to 
the frequency of oscillation of the current flowing in it. That is: wave length = the velocity of 
electricity -f- the frequency of the currents in the aerial. Since electricity travels at 300,000,000 meters 
per second, if it is determined lhat the current in the aerial is oscillating at 1,000,000 cycles per second, 
then 300,000,000 -f- 1,000,000 = 300 meters, the wave length radiated. Since the set illustrated in the 
photograph is designed to radiate wave lengths of 150, 200 and 250 meters it is seen that the frequency 
of oscillation of the currents in the aerial must be: 2,000,000 for 150 meters; 1,500,000 for 200 meters; 
1,200,000 for 250 meters. 

For successful operation with this extremely high frequency the rate of current oscillation must be 
the same in the certain parts of the apparatus which comprise the radio set. 

Recalling that depressing the key transfers the current from condenser and spark gap to the aerial, 
tv/o natural divisions of the complete circuit are evident, viz: 

Closed Circuit—Condenser-spark gap-oscillation transformer. 

Radiating Circuit—Oscillation transformer-aerial tuning coils-aerial and grounded circuit. 

These are termed the radio frequency circuits of the transmitter. To regulate the currents in these 
circuits so that their frequency is identical in both is the principal function of most of the apparatus 
which comprises the radio set. Adjustment of the two circuits to the required resonance will be de¬ 
scribed : 

CLOSED CIRCUIT 

The operator turns the knob Power Control (seen in the photograph, Figure 144, on top of the 
cabinet a trifle on the right of center). This simultaneously controls the output from the motor gen¬ 
erator and the number of plates of the spark gap to be connected in the circuit. The diagram, Figure 
145, shows how this is accomplished. The control rod when turned to the position P-1 leaves only a 
tew turns of wire in the field resistance coil to oppose the current from the exciter of the alternator, a 
larger proportion of its current output being thus obtained. At the same time the control has acted 
on the spark gap, cutting in most of its plates. When the control switch is thrown to position 
P-2, exactly the reverse happens: More turns in the resistance coil oppose the flow of current from 
the exciter, and less plates in the spark gap are left in circuit. The balance of adjustment for the closed 
circuit is made by the wave length changing switch (center top of cabinet in the photograph) which, 
as shown in the diagram, cuts in a fixed number of turns of the oscillation transformer when the 
switch is set to the selected contacts marked for 150, 200 or 250 meters. 

RADIATING CIRCUIT , 

It should be noted that the oscillation transformer also aids the adjustment for resonance between the 
closed and the radiating circuits. The diagram shows how additional closeness of adjustment is ob¬ 
tained in this circuit. The aerial tuning coils L-l and L-2 and L-3 connected to the contacts K-l, K-2 
and K-3 add the necessary turns for a progressive increase in wave length as the switch is moved on 
the contacts from 150 to 200 or 250 meters. The fine adjustment for complete resonance is obtained by 
the variometer coils, L-4 and L-5, which, when placed near or drawn away from each other, have the 
same effect as cutting in or out turns of coils L-l. L-2 and L-3. When the set is put into operation, 
the wave length desired is obtained by turning the knob controlling the aerial tuning coils (in the photo¬ 
graph, top left) until the ammeter’s needle gives the maximum reading. 

To the novice, wireless telegraphy and the apparatus used appears heavely technical. But a large 
part of the mystery will disappear if the aviator carefully re-reads the outline of the theory contained 
on this page and page 179, referring constantly to the diagram and bearing in mind the divisions made of 
the apparatus according to function. 








182 


Practical Aviation 



Tins remarkable airplane picture, considered by the military experts to be among the greatest ever taken 
°J tllc uwocst concentration camps at which munitions and men were assembled for the 1918 string 

onLwlv'lnfdllTrll' ? e p! S tlC f ° ffic A a r rcp °, rt W J la l ^Picture shows: 1 —Supply railway trains running 
neuly laid tracks. 2—Piles of supplies, chiefly timbers for use m building dugouts. 3—Rolls of barbed 

zone. 4 —1 ties of iron stakes for stringing barbed wire. 5 —Steel roofing for dugouts. 








Reconnaissance Photo of Enemy Base 


183 


6 Site of railway station. Note big shell craters (about sixty feet across ) caused by 420 M.M. shells. 

7 g 9 _ Remains of former railway trades where they entered railway station. 10 —Broken tics of former 

railway tracks. 11 —Other supplies' piled up. Perishable goods covered over with tent cloth. 12 —Battery of 
four guns, with abris for gunners. 13— Commander’s dugout. 14 —Ammunition park. Note enemy soldiers 

standing around, 15 —German soldiers standing in the road watching the airplane. 




184 


Practical Aviation 


AERIAL PHOTOGRAPHY 


Reconnaissance photography from airplanes is a tremendously important branch 
of the air service. Military maps upon which offensives are based are assembled from 
prints of various small sections of the theatre of operations, disclosing to the com¬ 
manding general the exact location of all enemy batteries, entrenchments and fortified 
positions, lines of transport and communication. By constant activity the camera men 
keep these maps accurate up to within a few hours. Expertness in photography re¬ 
quires considerable study and practical experience; but such skill is required only of 
specialists. Military observers and pilots are ordinarily required merely to arrive over 
the objective and snap the camera’s shutter. Some knowledge of photographic funda¬ 
mentals will be found useful, however. 

THE CAMERA AND ITS PARTS 

Camera—A light tight box with a lens at one end and a support for films or plates at the other. 
By means of a shutter objects are projected through the lens on the sensitive film for fractional inter¬ 
vals of time. Bellows, for folding the camera to smaller dimensions; stops, for regulating the projected 
rays, and various other attachments, are auxiliary devices. In airplane photography there are two main 
types of cameras, (a) automatic, (b) pistol. The automatic camera has regulating attachments which, 
when started, automatically make a series of consecutive views of the course of flight over the selected 
locality. By means of a guide line the points of union of two adjacent views is indicated, and from 
the focal angle of the lens and the altitude when exposure was made, a scale of distances is computed. 
The pistol type has the general form of that weapon and a trigger-operated shutter. It is used in flight 
for taking close-up photographs of enemy airplanes, from which construction details of new types may 
be secured. For training in aerial gunnery the pistol type of camera is also useful, being mounted 
rigidly on the plane and directed at other machines in flight, guide lines on the developed picture indi¬ 
cating the accuracy of aiming. 

Finder—A ground glass panel which indicates the limits of the camera’s field of vision, generally 
placed at the rear end of the camera or between and below the aviator’s feet. 

Lens—Curved and transparent glass arranged to cause the luminous rays to either converge or 
diverge on the film or plate. Lenses are (a) single, (b) double, (c) anastigmat. The latter have 
superiority over the others in illuminating and converging power and highest correction. 

Stops or Diaphragm Openings—The device which regulates the converging of the rays of light 
at or near the center of the lens, smaller openings cutting off other rays of light and making sharper 
and clearer images on the picture. Knowledge of the correct use of stops is essential to good photog¬ 
raphy. 

Films and Plates—These are strips of celluloid or glass plates coated with a film of salts sensitive 
to the chemical action of light. The emulsion is composed of salts of silver, bromide of potassium and 
gelatine. After exposure to the light, the bromide of silver is changed to a state where that part of 
the coating exposed, when placed in a solution known as developer, takes the form of metallic silver 
having a dark color. Introduction of a fixing solution (hyposulphite of soda and water) dissolves all 
the bromide of silver excepting the dark silver salts which carry the image of the object revealed 
by the exposure. This image appears as a negative, the same chemical actions transferring its dark 
portions to lighter ones on the photographic print paper. 


ARRANGEMENT OF CAMERAS 


In airplane photography for military purposes a favored arrangement provides 
for three cameras pointing downward, the field of vision of each ending precisely 
where its predecessor begins, affording a panoramic view of the locality photographed. , 
The control is automatic; the three shutters operate by a push button, pressure of a 
lever forward then removing the plates from the cameras. The same lever, pulled 
back, inserts the new plates and makes all ready for the next exposure. 
PHOTOGRAPHIC FLIGHTS 


Two or three times a day during the progress of hostilities, reconnaissance airplanes fly over the 
enemy territory to a depth of 10 to 15 miles, being engaged in photographic work sometimes 6 hours per 
day. Two types of airplanes are used; the two-seater with a speed of 120 to 140 miles per hour, 
escorted by a formation of fast combat machines, and the single-seater, which goes out with small combat 
patrols of three or four planes. The convoys are piloted by highly trained specialists in formation flying 
and air tactics. Prescribed actions for each machine in the formation are executed on a single signal to ! 
meet almost any form of attack; all of these evolutions have for their object the protection of the photo¬ 
graphing airplane, the chief duty of the escort being to shield the reconnaissance machine during the 
entire journey. Photography from single-seaters in small groups is of a scouting nature, to keep the 
maps at headquarters up to date. 

Military information contained in photographs made in the air is generally superior to the reports 
possible when only the naked eye is employed. Minute details, such as wagons on roads, are revealed in 
exposures made at 12,000 to 15,000 feet. Rain, thick mist and low-hanging cloud masses present con¬ 
ditions which make air photography usually impossible, but certain forms of mist impenetrable to the 
eye will be pierced by the camera lens. Best conditions are represented by clear skies or high cloud 
masses which reflect the light down. One of the special values of reconnaissance photographs is in 
revealing camouflage. Twin prints placed in a stereoscope show the solid objects in their proper per¬ 
spective, whereas the overhead camouflage cover appears flat. 


MAPPING FROM PHOTOGRAPHS. 

Immediately upon landing, the laboratory men dismount the cameras or secure the plates or films and 
rush with them to nearby developing rooms mounted on motor trucks. Within 15 minutes the negatives 
are developed. Without waiting for prints, the negatives are placed in a stereopticon or balopticon lantern 
and thrown on a screen. If the magnified view discloses a new enemy position, its location is quickly 
given to the artillery commander. Prints meanwhile are rushed to headquarters where a group of experts 
reduce them to scale, determine the overlapping lines and paste them together to form a photographic 
map. These maps show every detail of the enemy terrain and skilled artillery observers with magnifying 
glasses search them for all indications of new military works of importance. Scouting trips provide the 

pictures which keep the map continuously correct to within a few hours. 

, ,. Tlie c wjde area which may be mapped by airplane photography may be appreciated by consideration 

in non It t V1S ‘° n ,° f , a c . amera - J h, f 15 determined by the altitude, an 8-inch lens at a height of 

10,000 feet, for example, having a field of more than a square mile. 




.Practical Aviation 


185 


REVIEW QUIZ 

Reconnaissance and Fire Spotting 


What preparations are required of pilot and observer immediately 
upon receipt of orders for a reconnaissance flight? 

State the difference between a strategical and a tactical recon¬ 
naissance. 


About how many men will be in a column of infantry a mile long, 
marching in column of squads? Cavalry, in column of fours? 
How many of the infantry will pass a selected point in one 
minute? How many of the cavalry? 

State in detail the data required by the various headings of a recon¬ 
naissance report. 

Explain what is meant, in ranging for artillery, by the corrections 
for line, range and fuse. 

How are observers’ maps divided for location of objectives and why 
are both letters and numerals used? 


Describe the clock system of reporting shell hits. 

Give the direction of airplane flight which is most favorable for 
sending radio signals. During what airplane movement should 
they be suspended? 

How must the letters of the telegraph code be learned? 

What is the proper position of the hand on the key? 

Give the rule which governs the lengths of the dot and the dash. 

Give the abbreviations for “break,” “correction,” “ch,” “end of 
message.” 

Explain how the image is registered on a photographic film or plate. 

State the atmospheric conditions favorable and unfavorable to aerial 
photography. 

How are photographs employed to disclose camouflage? 

Classify the parts of a radio set into four divisions by function. 

Why must the high frequency current be regulated so the radiated 
wave will have a definite wave length? 

For generation of current for the airplane radio set described, why 
are both D. C. dynamo and A. C. dynamo required? 

What is the difference between a closed circuit and a radiating cir¬ 
cuit? 

What is meant by resonance between these two circuits and which 
parts of the apparatus establish it? 






186 


Practical Aviation 



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APPENDIX 


Nomenclature for Aeronautics 
With the French Equivalents and Phonetics 

The following glossary of terms will serve as a guide to the new and peculiar language of 
aeronautics. The definitions are largely taken from those prepared hy the National Advisory Com¬ 
mittee for Aeronautics. 

The French equivalents and phonetics for pronunciation have been checked hy French aviators. 
No key is needed ; where it has been possible to give the sound hy a short word or syllable, such 
as “day,” it is so given. Perfection in phonetics is impossible of achievement, for the reason that 
there are sounds in French which have no equivalent in English. But if the words are spoken as 
they read, no difficulty will be experienced in being understood. Where the small r and ny appears 
above the line, it indicates that the reader prepares to sound the word or syllable with the r or ny 
included, but cuts off the r or ny before it is actually spoken. This gives the peculiar sound to French 
words which is erroneously termed nasal. Those who speak English will have principal difficulty 

in pronouncing syllables which are here given phonetically as cur, dcu, pen. The exact sound is 
difficult of accomplishment without practice to develop the vocal chords. But it can be mastered to 
entire satisfaction if the lips are pursed as for whistling and held firmly while an attempt is made 
to sound the letter E. 

Aerofoil Aerofoil (m) (ah-ay-roh-foahl) : A winglike structure, flat or 
curved, designed to obtain reaction upon its surface from the air through 
which it moves. 

Aileron (Wing Flap) Aileron (m) (ay-le r -roh ns ) : A movable auxiliary sur¬ 
face used to produce a rolling motion about the fore and aft axis. 

Aircraft Aeronef (m) (ah-ay-roh-neff) Any form of craft designed for the 
navigation of the air—airplanes, balloons, dirigibles, helicopters, kites, kite 
balloons, ornithopters, gliders, etc. 

Aeroplane ^Aeroplane (m) (ah-ay-roh-plahn) : A form of aircraft heavier 

than air which has wing surfaces for support in the air, with stabilizing 
surfaces, rudders for steering, and power plant for propulsion through the 
air. This term is commonly used in a more restricted sense to refer to 
airplanes fitted with landing gear suited to operation from the land. If the 
landing gear is suited to operation from the water, the term “seaplane” is 
used. (See definition.) 

Airplane, Pusher Aeroplane a helice arricrc (m) (ah-ay-roh-plahn ah ay-leece 
ah-ree’air) : A type of airplane with the propeller in the rear of the wings. 

Airplane, Tractor Aeroplane a helice avant (m) (ah-ay-roh-plahn ah ay-leece 
ah voh ng ) : A type of airplane with the propeller in front of the wings. 

Air-speed Meter Metre a zhtesse (m) (met’trah’vee-tess) : An instrument 
designed to measure the speed of an aircraft with reference to the air. 

Altimeter Altimetre (m) (ahhtee’met’r) : An aneroid mounted on an air¬ 
craft to indicate continuously its height above the surface of the earth. 

Anemometer Anemometre (m) (ah-nee-moh-met’r) : Any instrument for 
measuring the velocity of the wind. 

Angle Angle (m) (au ng gel) : Angle. 

187 


188 


Practical Aviation 


7 


Angle of Incidence Angle coincidence (m) (au ng gel den-see-daunce) : I he 
acute angle between the direction of the relative wind and the chord of an 
aerofoil; i. e., the angle between the chord of an aerofoil and its motion rela¬ 
tive to the air. (This definition may be extended to any body having an axis.) 

Angle, Critical Angle d’attaque (m) (au ns gel dah’tack) : The angle of attack at 
which the lift curve has its first maximum; sometimes referred to as the 
“burble point.” (If the “lift curve” has more than one maximum, this refers 
to the first one.) 

Angle, Gliding Angle de descente (m) (au ns gel de r day’saunt) : The angle 
the flight path makes with the horizontal when flying in still air under the 
influence of gravity alone, i. e., without power from the engine. 

Appendix Appendix (m) (ah-pau ng dix) : The hose at the bottom of a balloon 
used for inflation. In the case of a spherical balloon it also serves for 
equalization of pressure. 

Aspect ratio Allongement (m) (ah-longe-mau ng ) : The ratio of span to chord of 
an aerofoil. 

Aviator Aviateur (m) (ah-vee'ah-teur) : The operator or pilot of heavier-than- 
air craft. This term is applied regardless of the sex of the operator. 

Axes of an Aircraft Essieux (m) (ess-seu) : Three fixed lines of reference; 
usually centroidal and mutually rectangular. The principal longitudinal 
axis in the plane of symmetry, usually parallel to the axis of the propeller, is 
called the fore and aft axis (or longitudinal axis) ; the axis perpendicular to 
this in the plane of symmetry is called the vertical axis; and the third axis, 
perpendicular to the other two, is called the transverse axis (or lateral axis). 
In mathematical discussions the first of these axes, drawn from front to 
rear, is called the X axis; the second, drawn upward, the Z axis; and the 
third, forming a “left-handed” system, the Y axis. 

Ballonet Ballonnet (m) (bah-loh-nay) : A small balloon within the interior 
of a balloon or dirigible for the purpose of controlling the ascent or descent, • 
and for maintaining pressure on the outer envelope so as to prevent de¬ 
formation. The ballonet is kept inflated with air at the required pressure, 
under the control of a blower and valves. 

Balloon Ballon (m) (bah’lon) : A form of aircraft comprising a gas bag 
and a basket. The support in the air results from the buoyancy of the air 
displaced by the gas bag, the form of which is maintained by the pressure 
of a contained gas lighter than air. 

Balloon, Barrage Ballon barrage (m) (bah’lon bah-rahge) : A small spherical 
captive balloon, raised as a protection against attacks by airplanes. 

Balloon, Captive Ballon captif (m) (bah’lon cap-tiff) : A balloon restrained 
from free flight by means of a cable attaching it to the earth. 

Balloon, Kite Ballon d’observation (m) (bah’lon dohps-sair-vah-see’oh ng ) : An 
elongated form of captive balloon, fitted with tail appendages to keep it 
headed into the wind, and deriving increased lift due to its axis being inclined 
to the wind. 

Balloon, Pilot Ballon pilote (m) (bah’lon pee-lot) : A small spherical balloon 
sent up to show the direction of the wind. 

Balloon, Sounding Ballon sonde (m) (bah’lon sohnd) : A small spherical 
balloon sent aloft, without passengers, but with registering meteorological 
instruments. 




Appendix 


189 


Balloon bed Ballon terrain d’attcrrissage (m) (bah’lon tay’rah 05 dah-tay-ree- 
sahge) : A mooring place on the ground for a captive balloon. 

Balloon cloth Ballon tissu pour toile caoutclioutee (m) (bah lon tee seu pool 
twahl cow-chew-tay) : I he cloth, usually cotton, of which balloon fabric? 

are made. 

Balloon Fabric: The finished material, usually rubberized, cf which balloon 
envelopes are made. 

Bank Gauchir (v) (go-sheer) : To incline an airplane laterally—i. e., to roll 
it about the fore and aft axis. Right bank is to incline the airplane with the 
right wing down. Also used as a noun to describe the position of an airplane 
when its lateral axis is inclined to the horizontal. 

Barograph Barograph (m) (bah-roh-graph) : An instrument used to record 
variations in barometric pressure. In aeronautics the charts on which the 
records are made indicate altitudes directly instead of barometric pressures. 

0 

Basket Nacelle (f) (nalrcell) : The car suspended beneath a balloon, for 

passengers, ballast, etc. 

Biplane Biplan (m) (bee’ploh ns ) : A form of airplane in which the main 
supporting surface is divided into two parts, one above the other. 

Body of an Airplane Fuselage (m) (feu’zeh-lahge) : The structure which 
contains the power plant, fuel, passengers, etc. 

Bonnet Bonnet (m) (bohn’ay) : The appliance having the form of a parasol 
which protects the valve of a spherical balloon against rain. 

Cabane Cabane (f) (kah’bahn) : A pyrmadial framework upon the wing of 
an airplane, to which stays, etc., are secured. 

Camber Courbure (f) (keer-beur) : The convexity or rise of the curve of an 
aerofoil from its chord, usually expressed as the ratio of the maximum de¬ 
parture of the curve from the chord to the length of the chord. “Top camber” 
refers to the top surface of an aerofoil, and “bottom camber” to the bottom 
surface; “mean camber” is the mean of these two. 

Center Centre (m) (saunt’r) Of pressure of an aerofoil. —The point in the 
plane of the chords of an aerofoil, prolonged if necessary, through which at 
any given attitude the line of action of the resultant air force passes. (This 
definition may be extended to any body.) 

Chord Corde (f) (kord) : Of an aerofoil section. —A right line tangent at 
the front and rear to the under curve of an aerofoil section. 

Length. —The length of the chord is the length of the projection of the 
aerofoil section on the chord. 

Clinometer (inclinometer) Jndicateur de pente (m) (ahn-dee-kah-teur de r 
paunt) : An instrument for measuring the angle made by any axis of an air¬ 
craft with the horizontal, often called an inclinometer. 

Controls Commandes (f) (koh-maund) : A general term applying to the 
means provided for operating the devices used to control speed, direction of 
flight, and attitude of an aircraft. 

Control column Levier de commande (m) (le r vee’ay de r koh-maund) : The 
vertical lever by means of which certain of the principal controls are operated, 
usually those for pitching and rolling. 







190 


Practical Aviation 


« 


Decalage Longitudinal V (m) (lohng-gee-teu-dee’nahl): The angle between 
the chords of the principal and the tail planes of a monoplane. The same 
term may be applied to the corresponding angle between the direction of the 
chord or chords of a biplane and the direction of a tail plane. (This angle is 
also sometimes known as the longitudinal V of the two planes.) 

Dihedral in an airplane Dicdre (a) (dee-ay’d'r) : The angle included at the 
intersection of the imaginary surfaces containing the chords of the right and 
left wings (continued to the plane of symmetry if necessary). This angle 
is measured in a plane perpendicular to that intersection. The measure of 
the dihedral is taken as 90° minus one-half of this angle as defined. The 
dihedral of the upper wing may and frequently does differ from that of 
the lower wing in a biplane. 

Dirigible Dirigeable (m) (dee-ree-zhah’bl) : A form of balloon, the outer 
envelope of which is of elongated form, provided with a propelling system, 
car, rudders, and stabilizing surfaces. 

Dirigible, Nonrigid Dirigeable Nonrigide (m) (dee-ree-zhah’bl noh-ree’zghid) : 
A dirigible whose form is maintained by the pressure of the contained gas 
assisted by the car-suspension system. 

Dirigible, Rigid Dirigeable Rigidc (m) (dee-ree-zhah’bl ree’zghid) : A dirigble 
whose form is maintained by a rigid structure contained within the envelope. 

Dirigible, Semirigid Dirigeable Semi-rigide (m) (dee-ree-zhah’bl se r -me-ree- 
zghid) : A dirigible whose form is maintained by means of a rigid keel 
and by gas pressure. 

Diving Rudder (elevator) Gouvernal de Profondeur (m) (goo-vair-nahl dJ 
proh-foh ng -dare) : A hinged surface for controlling the longitudinal attitude 
of an aircraft; i. e., its rotation about the transverse axis. 

Dope Enduire (v) (au Ilg dweer) : A general term applied to the material 
used in treating the cloth surface of airplane members and balloons to , 
increase strength, produce tautness, and act as a filler - to maintain air¬ 
tightness ; it usually has a cellulose base. 

Drag (drift) Derive (f) (day-reeve) : The component parallel to the rela¬ 
tive wind of the total force on an aircraft due to the air through which it 
moves. That part of the drag due to the wings is called “wing resistance” 
(formerly called “drift”) ; that due to the rest of the airplane is called “para¬ 
site resistance” (formerly called “head resistance”). 

Drift (see Drag) : Also used as synonymous with “leeway,” g. v. 

Drift-meter Metre de la derive (m) (met’r de r lah day-reeve) : An instru¬ 
ment for the measurement of the angular deviation of an aircraft from a set 
course, due to cross winds. 

Elevator (see Diving Rudder) 

Entering edge Bord d’attaque (m) (boar dah-tack) : The foremost edge of 
an aerofoil or propeller blade. 

Envelope Envelope (f) (envelope): The portion of the balloon or dirigible 
which contains the gas. 

Epannage (tail) Queue (f) (keu) : The rear portion of an aircraft, to 
which are usually attached rudders, elevators, stabilizers, and fins. 





Appendix 

t--——-—-- 


191 


Equator Equateur (m) (ay-quah-teur) : The largest horizontal circle of a 
spherical balloon. 

Float Flotteur (m) (flo’teur) : That portion of the landing gear of an air¬ 
craft which provides buoyancy when it is resting on the surface of the water. 

Gap Espace (f) (ess-pass) : The shortest distance between the planes of the 
chords of the upper and lower wings of a biplane. 

Glide Vol Plane (m) (vol plah’nay) : To fly without engine power. 

Glider Planenr (m) (plah’nair) : A form of aircraft similar to an airplane, 

but without any power plant. When utilized in variable winds it makes use 
of the soaring principles of. flight and is sometimes called a soaring machine. 

Guide rope Cordt a guider (f) (kord ah gid-day) : The long trailing rope 
attached to a spherical balloon or dirigible, to serve as a brake and as a 
variable ballast. 

Guy Hauban (m) (oh-bau ng ) : A rope, chain, wire, or rod attached to an 
object to guide or steady it, such as guys to wing, tail, or landing gear. 

Hangar Hangar (m) (au ng gahr) : A shed for housing balloons or airplanes. 

Helicopter Helicopterc (m) (ay-lee-copt-air) : A form of aircraft whose 
support in the air is derived from the vertical thrust of propellers. 

Inclinometer (see Clinometer) 

Horn Guignol (m) (ginn-yol) : A short arm fastened to a movable part of 
an airplane, serving as a lever-arm, e. g., aileron-horn, rudder-horn, elevator- 
horn. 

Inspection window Porte de visite (f) (port de r visit) : A small transparent 
window in the envelope of a balloon or in the wing of an airplane to allow 
inspection of the interior. 

Kite Cerf-volant (m) (sair-voh-loh ng ) : A form of aircraft without other 
propelling means than the towline pull, whose support is derived from the 
force of the wind moving past its surface. 

Landing gear Train (Tatterrissage (m) (trah ng dah-tay-ree-sahge) : The un¬ 
derstructure of an aircraft designed to carry the load when resting on or 
running on the surface of the land or water. 

Leeway Derive due au vent lateral (f) (day-reeve deu oh vau ng lah-tay-rahl) : 
The angular deviation from a set course over the earth, due to cros-s cur¬ 
rents of wind, also called drift; hence, “drift meter." 

Lift Poussee (f) (poo-say) : The component perpendicular to the relative 
wind, in a vertical plane, of the force on an aerofoil due to the air pressure 
caused by motion through the air. 

Load, dead Poids mort (m) (poo’ah more) : The structure, power plant, and 
essential accessories of an aircraft. 

Load, full Poids total (m) (poo’ah toh’tahl) : The maximum weight which 
an aircraft can support in flight; the “gross weight. 

Load, useful Poids utile (m) (poo’ah eu’teel) : The excess of the full load 
over the dead-weight of the aircraft itself, i. e., over the weight of its struc¬ 
ture, power plant, and essential accessories. (These last must be specified.) 




192 


Practical Aviation 


-I 


Monoplane Mono plan (m) (moh-noh-ploh nB ) : A form of airplane whose 
main supporting surface is a single wing, extending equally on each side of 
the body. 

Net Filet (m) (fee’lay) : A rigging made of ropes and twine on spherical 
balloons, which supports the entire load carried. 

Ornithopter Ornithophcre (m) (or’nee-top-tair) : A form of aircraft deriv¬ 
ing its support and propelling force from flapping wings. 

Parachute Parachute (m) (pah-rah-shoot) : An apparatus, made like an um¬ 
brella, used to retard the descent of a falling body. 

Permeability Permcabilite (m) (pair-may-ah-bee-lee-tay) : The measure of 
the loss of gas by diffusion through the intact balloon fabric. 

Pitot tube Tube de Pitot (m) (tueb de r peet’yoh) : A tube with an end open 
square to the fluid stream, used as a detector of an impact pressure. It is 
usually associated with a coaxial tube surrounding it, having perforations 
normal to the axis for indicating static pressure; or there is such a tube 
placed near it and parallel to it, with a closed conical end and having per¬ 
forations in its side. The velocity of the fluid can be determined from the 
difference between the impact pressure and the static pressure, as read by 
a suitable gauge. This instrument is often used to determine the velocity of 
an aircraft through the air. 

Pylon Pylone (m) (pee’lone) : A mast or pillar serving as a marker of a 
course. 

Relative wind Vent relatif (m) (vau ng ray’lah-tifif) : The motion of the air 
with reference to a moving body. Its direction and velocity, therefore, are 
found by adding two vectors, one being the velocity of the air with reference 
to the earth, the other being equal and opposite to the velocity of the body 
with reference to the earth. 

Rudder Gouvcrnail de direction (m) (goo-vair-nah’ee de r dee-reck-see-oh ng ) : 
A hinged or pivoted surface, usually more or less flat or streamlined, used 
for the purpose of controlling the attitude of an aircraft about its “vertical” 
axis, i. e., for controlling its lateral movement. 

Rudder bar Palonnier (m) (pah-lun’yay) : The foot bar by means of which the 
rudder is operated. 

Seaplane Hydroplane (m) (ee-droh-plahn) : A particular form of airplane in 
which the landing gear is suited to operation from the water. 

Side slipping Glissade sur Vaile (f) (glee-sahd seur fell) : Sliding downward 
and inward when making a turn; due to excessive banking. It is the opposite 
of skidding. 

Skids Bequilles (f) (bay-kee’e) : Long wooden or metal runners designed to 
prevent nosing of a land machine when landing or to prevent dropping into 
holes or ditches in rough ground. Generally designed to function should the 
landing gear collapse or fail to act. 

Slip stream (Propeller race) Vent de Vhelice (m) (vau ns de r lay-leece) : 
The stream of air driven aft by the propeller and with a velocity relative to 
the airplane greater than that of the surrounding body of still air. 

Soaring machine Planeur (m) (plah’nair) : See Glider. 





Appendix 


193 


Span (spread) Envergure (f) (au ng vair-geur) : The maximum distance lat¬ 
erally from tip to tip of an airplane wing, or the lateral dimension of an 
aerofoil. 

Stability Stabilite (f) (stah-bee-lee-tay) : A quality in virtue of which an 
airplane in flight tends to return to its previous attitude after a slight dis¬ 
turbance. 

Stability, Directional Stability en direction (f) (stah-bee-lee-tay au ns dee-reck- 
see-oh ns ) : Stability with reference to the vertical axis. 

Stability, Dynamical Stability dynamique (f) (stah-bee-lee-tay dee-nah-mick) : 
The quality of an aircraft in flight which causes it to return to a condition 
of equilibrium after its attitude has been changed by meeting some disturb¬ 
ance, e. g., a gust. This return to equilibrium is due to two factors; first, 
the inherent righting movements of the structure; second, the damping of the 
oscillations by the tail, etc. 

Stability, Inherent Stabilite inherente (f) (stah-bee-lee-tay a ng ay-raunt) Sta¬ 
bility of an aircraft due to the disposition and arrangement of its fixed parts; 
i. e., that property which causes it to return to its normal attitude of flight 
without the use of the controls. 

Stability, Lateral Stabilite laterale (f) (stah-bee-lee-tay lah-tay-rahl) : Sta¬ 
bility with reference to the longitudinal (or fore and aft) axis. 

Stability, Statical Stabilite statiqne (f) (stah-bee-lee-tay staht-tick) : In wind 
tunnel experiments it is found that there is a definite angle of attack so 
that for a greater angle or a less one the righting movements are those which 
tend to make the attitude return to this angle. This holds true for a 
certain range of angles on each side of this definite angle; and the machine 
is said to possess “statical stability” through this range. 

Stabilizer Plan fixe de queue (m) (ploh ng fix de r keu) : Any device designed 
to steady the motion of aircraft. 

Stagger Decal age des ailes (m) (day-kah-lahge dayzail) : The amount of 
advance of the entering edge of the upper wing of a biplane over that of the 
lower, expressed as percentage of gap; it is considered positive when the 
upper surface is forward. 

Stalling Perte de vitesse (f) (pert de r vee’tesse) : A term describing the con¬ 
dition of an airplane which from any cause has lost the relative speed neces¬ 
sary for control. 

Statoscope S tat os cope (m) (stah-toh-scup) : An instrument to detect the ex¬ 
istence of a small rate of ascent or descent, principally used in ballooning. 

Stay Haubans (m) (oh-bau ng ) : A wire, rope, or the like used as a tie piece 
to hold parts together, or to contribute stiffness; for example, the stays of 
the wing and body trussing. 

Step Ressaut (m) (resso) : A break in the form of the bottom of a float. 

Strut Montant (m) (moh ng -tau ng ) : A compression member of a truss frame; 
for instance, the vertical members of the wing truss of a biplane. 

Tail Queue (f) (keu) : See Epannage. 

Thimble Cosse (f) (koss) : An elongated metal eye spliced in the end of a 
rope or cable. 






194 


Practical Aviation 


Trailing edge Bord dc sortie (m) (bore de r sor’tee) : The rearmost edge of 
an aerofoil or propeller blade. 

Triplane Triplan (m) (tree-plah ng ) : A form of airplane whose main sup¬ 
porting surface is divided into three parts, superimposed. 

Truss Poutre armee (f) (poo’trahr-may) : The framing by which the wing 
loads are transmitted to the body; comprises struts, stays, and spars. 

Warp Gauchir (v) (go-sheer) : To change the form of the wing by twisting it. 

Wash out Reglage de Vincidence (m) (ray-glahge de r lence-see-daunce) : A 
permanent warp of an aerofoil so that the angle of attack decreases toward 
the wing tips. 

Wings Ailes (f) (ale) : The main supporting surfaces of an airplane. 

Wing flap Aileron (m) (ale-le r roh ng ) : See Aileron. 

Wing mast Mat (m) (mah) : The mast structure projecting above the wing, 
to which the top load wires are attached. 

Wing rib Nervure (f) (ner’veur) : A fore and aft member of the wing 
structure used to support the covering and to give the wing section its form. 

Wing spar (wing beam) Longeron (m) (loh ng -zher-roh ns ) : A transverse 
member of the wing structure. 

Yaw Louvoyer-mouvement de lacet (m) (loo-vwah-yay move-mau ng de r 
lah’say) : To swing off the course about the vertical axis. 

Angle of. —The temporary angular deviation of the fore-and-aft axis 
from the course. 


METRIC CONVERSION TABLES 


1 kilometer = 0.6214 mile. 

1 meter= 3.2808 feet. 

1 centimeter = 0.3937 inch. 

1 sq. meter =10.764 sq. feet. 

1 sq. centimeter = 0.155 sq. inch. 

1 cub. meter=35.314 cub. feet. 

1 liter = 0.0353 cubic foot. 

1 kilogram = 2.2046 pounds. 


1 mile= 1.609 kilometers. 

1 foot=0.3048 meter. 

1 inch = 2.54 centimeters. 

1 sq. foot=0.0929 sq. meter. 

1 sq. inch = 6.452 sq. centimeters. 

1 cub. foot = 28.317 liters. 

1 U. S. gallon = 3.785 liters. 

1 pound = 0.4536 kilogram. 


RULES FOR MENSURATION 

Triangle—Area equals one-half the product of the base and the altitude. 

Parallelogram—Area equals the product of the base and the altitude. 

Irregular figure bounded by straight lines—Divide the figure in triangles, and find the area of each triangle 
separately. The sum of the areas of all the triangles equals the area of the figure. 

Circle—Circumference equals diameter multiplied by 3.1416. 

Circle—Area equals diameter squared, multiplied by 0.7854. 

Circular arc—Length equals the circumference of the circle, multiplied by the number of degrees in the 
arc, divided by 360. 

Circular sector—Area equals the area of the whole circle multiplied by the quotient of the number of 
degrees in the arc of the sector divided by 360. 

Circular segment—Area equals area of circular sector formed by drawing radii from the center of the 
circle to the extremities ot the arc of the segment, minus area of triangle formed by the radii 
and the chord of the arc of the segment. 

Prism—Volume equals the area of the base multiplied by the altitude. 

Cylinder—Volume equals the area of the base circle times the altitude. 

Pyramid or Cone—Volume equals the area of the base times one-third the altitude. 




INDEX 


A 

Accuracy and Volume of Fire. 

Active Drift . 

Advanced Flying .. 

Aerial Combat .. 

Aerial Fountain, Cascade, Cataract, 

Breakers . 

Aerial Gunnery .. 

Aerial Photography (see Photography) 

Aerial (Radio) . 

Aerobatics and Night Flights . 

Aerofoil, The . 

Aerography . 

Ailerons . 

Ailerons, Rigging the . 

Air, Characteristics of the . 

Composition of the . 

Air Cooling ... 

Air, Flow of . 

Airdromes . 

Airplane Design, Elements of . 

Air Screw . 

Air Speed Meter . 

Aligning the Airplane . 

Alignment Errors, Effect of. 

Alternating Current . 

Altimeter ... 

Altitudes, Warfare . 

Alto-Stratus and Altocumulus Clouds 

Aluminum . 

Ammunition and Fire Correction 

Ampere, Definition of . 

Angles of Fire, Effective . 

Angle of Incidence . 

Verifying the . 

Angle of Incidence Indicator . 

Angles of Incidence in Flight . 

Antenna (Radio) . 

Anti-Aircraft Guns and Fire. 

Anti-Cyclone . 

Anzani Engine . 

Apparatus, Airplane Radio . 

Armament, Heavy Airplane . 

Armor for Airplanes . 

Artillery Fire, Directing . 

Ash .. 

Aspect Ratio . 

Assembly of Lifting Surfaces . 

Atmospheric Pressure . 

Attack, Skill in .. 

Attacks on Balloons . 

Aviation Wire and Strand. 

B 

Balloons, Attacks on . 

Banking . 

Banking Indicator .. . . . . 

Bank, Vertical . 

Barometer . 

Barrel . 

Battle Reconnaissance.,. 

Bearing . 

Bearings, Lost ... 

Beaufort Scale . 

Bending Materials . 

Billows, Wind . 

Bombing Airplane Types . 

Bombing Air Raids .. 

Bombing Crews, Training . 

Bombs and Bombing . 

Bomb Dropping . 

Bombs, Types of . 

Browning Gun, The . 

Bullets, Types of . 

Bumps .. 


c 

Cables and Wires, Control . 

Camber . 

Camera and Its Parts, The 

Cams . 

Camshaft ..'. 

Canard Principle . 

Carburetion and Carburetors 

Care of Engines . 

Cavaro . 

Cedar . 

Cellon . 

Center of Gravity . 


Page 
.... 152 
. . . . 6 
107, 127 
. . . . 147 

.... 141 
.... 147 

.... 181 
.... 127 
. . . . 4 

. . . . 137 
...3, 27 
.... 46 

.... 138 
. . . . 4 

.... 75 

. . . . 7 

. ... 113 
. . . . 13 

. ... 53 

.... 100 
.... 44 

.... 48 

.... 179 
.... 97 

.. . . 159 
. . . . 143 
.... 38 

. . .. 153 
.... 179 
.... 155 
... 5, 8 
.... 45 

.... 99 

. . . . 18 
.... 181 
.... 162 
.... 138 
.... 85 

.... 181 
.... 161 
.... 161 
177, 178 

- 36 

. . . . 9 

.... 43 

.... 138 
. . .. 157 
.... 163 
.... 38 


. 163 
3, 27 
. 100 
. 131 
. 97 
. 131 
. 172 
. 119 
. 122 
. 139 
. 34 
. 141 
. 165 
. 165 
. 165 
. 147 
. 166 
. 168 
. 151 
. 153 
. 141 


47 
4, 8 
184 
66 
66 
25 
68 
76 
37 

36 

37 
22 

195 


Chord, The . 

Circuit Breaker . ,... 

Circuit (Radio) : 

Closed . 

Radiating . 

Cirrus Family of Clouds. 

Clerget Engine . 

Climb, Angle of Best. 

Climb, Design for Maximum. 

Climbing . 

Clinometer . 

Clock System of Signaling. 

Closed Circuit (Radio) . 

Clothing, Aviator’s . 

Clouds, Classification of . 

Clouds, Fogs and Storms, Avoiding 

Cockpit Arrangement . 

Code, General Service, International, 

Continental . 

Code Signals for Artillery Control . 
Code Telegraphing, Instruction in . 

Combat, Aerial . 

Combat Rules .. 

Combustion Chamber . 

Compass, The . 

Compass, Use of and Adjustment . . 

Compression Stroke . 

Concentration, Theory of . 

Condenser, Motor Ignition . 

Radio . 

Connecting Rod . 

Conservation, Fuel . 

Contact Patrol . 

Continental Code . 

Contour . 

Control, Stick and Dep. 

Conventional Map Signs . 

Cooling, Water and Air. 

Cord, Tinned Aviator... 

Correction of Machine Gun Fire . .. 

Copper .. 

Course, Laying off a . 

Courses, Flying. 

Cranking the Engine . 

Crank Shaft. 

Ci’ank Shaft and Crank Case. 

Crew, The Flying . 

The Repair . 

Crews, Training Bombing . 

Cross-Country Flight . 

Crystallization and Fatigue . 

Cumulus Clouds . .. 

Curtiss Engine . 

Current, A. C. and D. C. 

Cyclone . 

Cylinder, Gasoline Engine . 

D 

Datum . 

Defects, Cause of Flight. 

Dep Control . 

Depressions, Secondary . 

Design, Elements of Airplane. 

Diaphragm Openings, Camera . 

Dihedral, Main Surface. 

Dihedral Angle, Longitudinal. 

Securing the . 

Direct Current . .. 

Directional Stability . 

Distributor. 

Dives, Nose . 

Dope . . . 

Drift, Calculating Wind . 

Lift and . 

Drift Meter . 

Droop . 

Dual Control Instruction . 

Dynamo, D. C. and A. C. .. . ; . 

E 

Eddies, Vertical Wind . 

Eight j Cylinder Motor. 

Elasticity of Air. 

Elevator, The . 

Elevators, Rigging of . 

Emaillite .•. 

Engineer, The Motor . 

Engines, Multiple Cylinder . 

Equipment for Night Flying . 


Page 

5 

. 74 

. 181 
. .181 
. 143 
. 85 
. 18 
. 16 
. Ill 
. 99 
. 178 
. 181 
. 95 
. 143 
. 122 
. 96 


. . . . 174 
.... 177 
.... 175 
. . . . 147 
. . . . 157 
. . . . 55 

. . . . 97 

. . . . 117 
.... 56 

.... 159 

_■ 74 

. ... 181 
. .55, 64 
.... 87 

.... 161 
. . . . 174 
.... 119 
.... 29 

. . . . 118 
.... 75 

. . .. 38 

. . . . 153 
.... 38 

. . . . 121 
. . . . 104 
. . . . 86 
. . . . 55 

. . . . 65 

. . . . 109 

.... no 

. . . . 165 
103, 115 
. ... 38 

. . . . 143 

. 81 

.... 179 
. ... 138 
.... 55 


.... 119 
. . . . 48 

,... 29 

. . . . 139 
. . . . 13 

. . . . 184 
.... 25 

. . . . 24 

. . .. 45 

. . . . 179 
. ... 21 
.... 74 

.... 129 
.... 37 

.... 121 
. . . . 6 
. . . . 100 
.. . . 46 

.... 105 
179, 181 


141 

81 

4 

3 

42 

37 

109 

58 

133 






































































































































































Page 

Equivalent, Horizontal . 15 

Erection and Assembly . 42 

Estimates of Enemy Strength . 172 

Exciter, Radio . 181 

Exhaust Stroke. 56 

Expanding Bullets . 153 

Explosive Machine Gun Bullets . 153 

F 

Factor of Safety . 33 

Factor, to Determine Wind. 121 

Fatigue, Crystallization and. 38 

Ferrules, Metal for . 38 

Field Resistance (Radio) . 181 

Films and Plates, Camera . 184 

Finder, Camera. 184 

Fire, Accuracy and Volume of . 152 

Correction of Machine Gun . 153 

Directing Artillery . 177, 178 

Effective Angles of. 155 

Spotting . 171 

Firing Order of Engines. 58, 59 

Flaps, Wing .3, 27 

Flares . 165 

Flat Turn . 132 

Fleet, Employment of the Air. 159 

Flight. Theory and Principles of. 1 

Float-Offs . Ill 

Flow of Air . 7 

Flying, Instruction in . 103 

Forced Landings . 123 

Force-Feed Lubrication . 76 

Formation, Flying in . 158 

Four-Cycle Principle . 56 

Four-Cylinder Operation . 58 

Fuselage, The . 3 


G 

Gauges . 96 

General Service Code . 174 

Generating Electrical Power (Radio) . 181 

Generator, Radio . 181 

Gnome Engine .. 85 

Goggles, Aviator’s . 95 

Gradient . 119 

Grass-Cutter . 107 

Gravity, Center of . 22 

Grip, Proper Telegraphing . 175 

Ground, Radio Apparatus . 181 

Ground, Signals From the . 178 

Ground Targets . 152 

Gunner, The . 109 

Gunnery, Aerial . 147 

Gusts, Wind . 141 

x H 

Hachures . 119 

Head Resistance . 7 

Helicopter, The . 1 

Helpers, Mechanician . 110 

Hickory . 36 

Horizontal Equivalent . 15 

Horizontal Stabilizer, Rigging of . 42 

I 

Ignition, Cooling and Lubrication . 73 

Immelman Turn . 132 

Incendiary Bombs .. 168 

Incidence, Angle of . 5 

Inclinometer . 99 

Indicators .99, 100 

Inertia, Air . 4 

Information, Gathering . 172 

Instability, Causes of. 48 

Instruments and Equipment for Flight .... 94 

Intake Stroke . 56 

International Code . 174 

J 

Joy Stick . 29 

Junior Military Aviator Tests . 104 

K 

Ivey. Radiotelegraph . 181 

Kilowatt, Definition of . 179 

Knocking, Engine . 92 

L 

Landing at Night. 134 

Landing Gear, Assembly of . 42 

Landing Sites . 113 

Landings . 114 

Forced . 123 


Page 

Landmarks . 122 

Lateral Stability . 21, 26 

Layers, Wind. 141 

Leaving the Ground. Ill 

Lens, Camera . 184 

Le Rhone Engine .* 85 

Lewis Machine Gun, The. 151 

Liberty Motor, The . 82 

Lift and Drift. 6 

Lift-Drift Ratio . 7 

Lifting Surfaces, Assembly of . 43 

Lighting the Field at Night. 134 

Line Squalls . 139 

Longitudinal Stability. 21, 23 

Loop the Loop. 130 

Loop, Spiral . 132 

Loops, Wire. 47 

Lubrication of Engines . 76 

Luminous Dials. 96 

M 

Machine Gun, The Lewis. 151 

Magneto . 74 

Magneto Timing . 73 

Mahogany . 36 

Maple . 36 

Map Reading. 119 

Map, Weather. 139 

Mapping From Photographs . 184 

Materials, Stresses and Strains . 33 

Mechanician, Aviation . 110 

Meridian . 119 

Metal Fittings and Wire. 38 

Meteorology for the Airman . 137 

Meters . 100 

Military Aviator Flying Course. 106 

Minimum Angle . 18 

Missing, Engine . 90 

Monel Metal . 38 

Monoplane, The . 3 

Motive Power, Fundamentals of. 51 

Motor Engineer. 109 

Motors, Types, Operation and Care. 76 

Mountings, Machine Gun . 155 

Mufflers . 165 


N 


Nacelle, The . 3 

Navigator, The . 109 

Night Flights . 127 

Night Flying . 133 

Nimbus Clouds . 143 

Nose Dive . 129 

Novavia . 37 

N-Square Law . 159 


o 

Observer, The . 109 

Observer’s Maps for Fire Spotting. 177 

Operation of Engines. 76 

Operator, The Radio . 109 

Optimum Angle . 18 

Orders for Flights . 172 

Orienting a Map. 119 

Ornithopter, The. l 

Oscillation Transformer (Radio) . 181 


P 

Pancake, The . 114 

Passive Drift. 6 

Pegging Down .] 124 

Penguin . 107 

Perforating Bullets . 153 

Photographic Flights . 134 

Photographs, Mapping From .! 184 

Physical Fitness . 115 

Pilot. The .i 109 

Pine, Hard . 36 

Piston ...! ! 55 

Piston Rings . 04 

Pistons, Valves and Carburetors .!. ! ! 63 

Pitching . 3 

Plates and Films, Camera .* *184 

Power, Fundamentals of Motive . 51 

Stroke . 50 

Preparations for Reconnaissance Flights ... 172 

Preparatory Reconnaissance. 173 

Pressure and Suction, Lift by Air..* 5 

Pressure Areas . .. 138 

Primary of Transformer (Radio) .!!! 181 

Principles of Flight, Theory and. 1 

196 


































































































































































Propeller . 53 

Propeller, Swinging the . 86 

Protective Reconnaissance . 172 

Pusher Airplane . 2 


Quenched Spark Gap (Radio) . 181 

Quiz, Review : 

Aerial Gunnery and Combat—Bombs 

and Bombing. 169 

Aerobatics and Night Flights . 135 

Elements of Airplane Design . 19 

First Flights and Cross-Country Flights 125 

Flight Stability and Control. 30 

Fundamentals of Motive Power. 61 

Ignition, Cooling and Lubiucation of 

Engines ... 77 

Instruments and Equipment for Flight 101 

Materials, Stresses and Strains . 39 

Meteorology for the Airman . 145 

Pistons, Valves and Carburetors . 71 

Reconnaissance and Fire Spotting .... 185 

Rigging the Airplane. 49 

Theory and Principles of Flight. 11 

Types of Motors, Operation and Care 
of Engines . 93 

R 

Radiated Wave (Radio) ... 181 

Radiating Circuit (Radio) . 181 

Radiator Temperature Indicator . 99 

Radio Apparatus, Airplane . 181 

Radio Operator, The . 109 

Radio Receivers . 179 

Radiotelegraphy, Theory of . 179 

Radius of Action . 122 

Range Finders for Bombing . 166 

Ranging, Artillery . 177 

Ratio, Aspect . 9 

Rudder, Rigging of . 42 

Reaction, Air . 6 

Receivers, Radio . 179 

Receiving Code . 175 

Reconnaissance and Fire Spotting . 171 

Reconnaissance by Airplane. 172 

Repair Crew, The . 110 

Reports of Flights . 173 

Resistance Coil (Radio) . 181 

Re-Starting . 124 

Review, Quiz (see Quiz) 

Revolution, An Engine. 55 

Rigging the Airplane. 41 

Right of Way in the Air . 113 

Rolling . 3 

Roll Over . 131 

Rotary Engines . 85 


S 

Safety Belt . 

Safety, Factor of . 

Scale, Beaufort . 

Scale, The Map . 

Screw, Air . 

Secondary Depressions . 

Secondary of Transformer (Radio) 

Self Starters . 

Sending Code . 

Shearing . 

Shells, Artillery . 

Signals, Code for Artillery Control 

Signals From the Ground. 

Six-Cylinder Operation . 

Skid, The . 

Skin Friction . 

Skipping, Engine . 

Solo Method of Flying . 

Span . 

Spark Gap (Radio) . 

Spark Plug . 

Speed, Design for Maximum. 

Speed Meter. Air. 

Spinning Nose Dive . 

Spiral . 

Spiral Loop . 

Splash Lubrication . 

Spruce . 

Squalls, Line .. 

Stability and Control, Flight. 

Stabilizers, Rigging of. 

Stagger . 

Stagger, To . 

Start of Flight, The . 


95 

33 
139 
119 

53 

139 

181 

87 

175 

34 
177 

177 

178 
59 

132 

6 

90 

106 

5 

181 

74 

17 

100 

129 

129 

132 

76 

36 

139 

21 

42 

10 

131 

111 


Starting, Re- . 

Starting the Engine . 

Steel . 

Steering Direction, Determining the 

Stick, Joy . 

Stops, Camera . 

Straightening Out . 

Strategical Reconnaissance . 

Strategy . 

Strato-Cumulus Clouds . 

Strength, Estimates of Enemy .... 

Stresses and Strains . 

S-Turns . 

Surface, The . 

Swinging the Compass . 

Swinging the Propeller . 


T 

Tachometer . 

Tactical Reconnaissance . 

Tactical Skill . 

Take-Offs . 

Taking-Off and Flying at Night 

Tanks, Metal for ’. 

Targets, Firing at Ground .... 

Taxying . 

Telegraph Key, Radio . 

Tests, Aviator . 

Theory and Principles of Flight 

Theory of Concentration . 

Thrust, The . 

Time Checking . 

Timing, Valve and Magneto . . 

Tin . 

Tinned Aviator Cord . 

Titanine ... 

Tool Chest, Airplane . 

Torrents, Aerial . 

Torsion . 

Tracing Bullets . 

Tractor Airplane. 

Transformer (Radio) . .. 

Triplane, The . 

Trouble Chart, Engine. 

Turn. Flat . 

Turnbuckles . 

Turning . 

Twelve-Cylinder Motor . 

U 

Undercarriage, Assembly of 
Upside Down Flying . 

V 

Valve Timing .'. 

Valves, Engine. 

Velocity . 

Velocity, Design for Maximum 

Vertical Rank . 

Vertical Stabilizer. Rigging of . 

Vertical Wind Eddies . 

V-Formation, Flight in . 

Viscosity of Air . 

Visual Signaling . 

Volt, Definition of . 

Volume of Fire, Accuracy and 
V-Type Motors . 


Page 
. 124 
. 86 
. 38 
. 121 
. 29 
. 184 
. 112 
. 173 
. 149 
. 143 
. 172 
. 33 
. 112 
4 

. 117 
. S6 


97 

172 

159 

111 

134 

38 

152 
111 
181 
104 

1 

159 

2 

124 

73 

38 

38 

37 

115 

141 

34 

153 


181 

o 

89 

132 

47 

112 

81 


42 

130 


. . 73 

66 , 67 
7 

. . 17 

. . 131 
. . 42 

. . 141 
. . 158 
4 

. . 175 
. . 179 
. . 152 
. . 81 


w 

Walnut .. 

Warfare Altitudes . 

Warping . 1 . 

Washin . 

Washout . 

Water Cooling. 

Wave Length (Radio) . 

Weather Map . 

Wedge. The . 

Wind Factor, Diagram to Determine 

Wing Covering . 

Wing Flaps . 

Wire for Airplanes . 

Wire, Metal Fittings and . 

Wireless Apparatus, Airplane . 

Wireless Telegraphy, Theory of 

Wires, Control Cables and. 

Wood, Strength of . 

Woods for Airplanes . 

Wrist Pin . 


Zooming 


z 


, 36 
159 
3 

, 27 
. 27 
75 

. 181 
. 139 
. 139 
. 121 
37 
3, 27 
. 38 
. 38 
. 181 
. 179 
47 
. 35 
. 36 
. 64 


131 


































































































































































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